Trying to tackle a lean-off idle spot. Yes, my accelerator pump is working correctly, tried multiple slots. I have the largest squirter installed (.043"). That actually did seem to help and make the car quite drivable.
Anyhow, I'm now looking closer at my idle screws. I was told to measure how far from "in" did I set them. The only on the left is 3 1/2 turns, and the one on the right is about 4 turns.
Obviously I set them by highest vacuum/RPM, so they are set appropriately. At least by how I believe should be set which is find the highest point, and slowly tighten until the RPM changes (drops).
I tried to reset them and ended up at the same spot. about 17" of vacuum, which is pretty healthy and a steady needle to go along with it.
Do these screws seem out by a lot to anyone else? I heard at 3-turns they are pretty much fully open at that point.
Plugs look really good. Slightly on the lean side.
:popcorn:
I too have battled this problem
First thought is have you checked the float level , if it is low it may not get fuel into the boosters fast enough causing a bog , CHECK this 1st
The other issue is the accelerator pump circuit so you have 3 different squirters & 3 positions on the arm , closest to the pivot adds the most fuel so that is where you need to be , the squirter still may not be big enough , in the past I have had to use numbered drillls & open up the squirter to make it work right
I wont mntion that Holley style carbs have 14 different cam positions instead of 3 & 12 different size squirters instaed of 3 ... Oh wait I guess I just did :Thud:
I tried the "richer" position of the AVS arm, and it didn't make a difference. I moved it back to the center point.
I thought about drilling out the .043" larger, but I'd hate to F*@ it up.
I was very diligent in checking float level...I think I did it twice and used the chart from Mike's Carb.
I'll remove the air horn and check this again eventually.
How about metering rods? Is there a certain way to do a "check" on those to verify that the pistons/springs are moving as they should under a blip of throttle?
On the idle mix screws, I did not "turn them back in" 1/8-1/4 of a turn from max-idle location. They are set right at the point that if they went back in, the RPM would drop. What's the process here? Still turn them in 1/8-1/4, and allow the idle to drop a little bit?
It appears you are running lean at idle. 3-1/2 and 4 turns out is excessive and indicates a problem somewhere. If you continue to back out the mixture screws to say 5 turns, will the idle rpm decrease due to an over rich condition or does the rpm stay the same? The idea is to have carburetor adjustability from too rich/too lean. :alan2cents:
I recall the float level is 7/32 , you could raise it 1/32 , it will help
Metering rods will not affect off idle , but if you undo the plate above the rod & swing it partially out of the way they rods should be down at idle & rise when you open the throttle , you can change the spring under the rods so they respond quicker , or stay down at idle if they are not but with the idle vacuum you have they will be staying down ok .
I would set the idle screws the way you did just before the idle speed drops as you turn them in , A smaller air bleed size would make the idle more sensitive so you might not have to turn them out that far But you cannot change the bleed size unless you crimp it closed with a vice grip . I have often removed the idle screws with zero change & yes that indicates a problem .
you could source another squirter nozzle & drill it out bigger , Eddy will sell you a set of 3 , small medium & large , you could stretch the small one bigger & try it , I bet it will work better .
could be Idle transition slots are exposed... solution is to back off the idle screw which may or may not require more advanced timing
about half way down in this article
http://www.superchevy.com/how-to/45638/
Item #2 is a transition slot
(https://forum.e-bodies.org/proxy.php?request=http%3A%2F%2Fimage.superchevy.com%2Ff%2F9559852%2Bw640%2Bh426%2Bq80%2Bre0%2Bcr1%2Bar0%2Bst0%2Fp109594_image_large.jpg&hash=fcfe3a24ee7482a378c7c930586d3a18fafc4b90)
I assume this is an OEM AVS. Mixture screws out 3 1/2 to 4 turns is normal. Make sure the pump plunger stem height is at least as high up as factory spec. If it is then try running it a LITTLE higher-this will send more fuel through the pump shooter-and possibly eliminate the tip in stumble. Sometimes lowering the stem height works too. Stem height is altered by bending the pump rod. This has worked for me in the past. A local friend/carb tinkerer around here has had good luck swapping the factory leather pump plunger for the Eddy 800 AVS version. He claims this has gotten rid of the tip in stumble on 2 different occasions. Also, when you change position with the pump rod(say moving it to the top hole), you should reset the pump plunger stem height.
And yes, what Chryco says is correct-making the air bleeds smaller or increasing the size of the idle feed restriction works. The 625 version is inherently lean, much more so than the 750 version..
One other thing-make sure the "s" link on top of the plunger stem is not installed backwards. Easy mistake to make...
Something else as well, quadrajetparts.com lists no less than 6 different sizes of leather-cupped pump plungers for oem AVS's. These are broken down by carb number. Make sure yours is right.
Wow, a lot of awesome responses.
The "S" link was backwards. I put it back correctly. This won't effect the performance of the accelerator pump though, but the longevity.
I will check out to see if my pump stem height is 7/16 (or 5.55mm). I'll report back on that.
Yea, I could drill out my smallest pump squirter from the kit if it came down to it.
Tempted to throw my big-block AVS on the car, but then that's just a damned shortcut. :)
Houston, I think we found our problem (I hope).
Time to start bending the rod?
Edit: Sorry, I converted this backwards. 7/16" is spec, or 11.11mm.
That makes more sense. Looks like I can raise this puppy up a little....about .4mm off...
Just a tad low. Make sure your choke/fast idle is not engaged when you take that measurement. Bending the top part of the pump rod inward will raise the stem height. If you go to high you will raise the plunger out the fuel in the bowl..Be patient with the bending, it can be maddening lol
I went out and rechecked and looks like I'm in spec. I don't understand how the fast idle linkage works. I took a picture of how it looks when I measured.
Looks like the pump height is correct.
I'm now considering to change the linkage hole for a faster shot and adjust the pump height.
Bottom hole is quicker shot, correct?
Fast idle is not engaged in that photo(screw that is facing downward engages the fast idle cam-the choke has to shut move all of the linkage). You say the "s" link was backwards and you switched it? Drive it and see if this makes a difference-it might. If it's still the same, I would try lowering the pump stem a little and leave the pump rod in the middle hole. It's important to only make one change at time when doing this kinda stuff..
Sounds good.
Yep, The "S" link didn't make a difference in drive-ability.
I'll move the pump down a tad. What would you suggest? It's basically at the stock position now.
I just moved it to the top most hole and set the height to 11.1mm or so. Doesn't take long to do.
NOT setting the height after that is a must, because if you don't set the height and just move the linkage to the top hole, you'll be nearly 14mm of pump height.
Going out for a drive!
Didn't seem to get better or worse. Still there.
Here's a video of it.
Options:
1) Lower the pump by a milimeter? Keep pump in "rich" position.
2) Recheck float heights. According to my chart, they should be set to 7/32".
3) Start drilling out spare squirt nozzle. to .045-.047
Took the air-horn off. The float height I'm measuring at 7/32. In-fact, probably a little smaller than that because sliding a 7/32" bit under the rear of the float lifts it ever so slightly. So Chryco, it sounds like this is where you would leave it since it is a bit smaller than 7/32" which means there should be enough fuel in the bowl.
At this point, my only option is to either reassemble and fudge with the height of the pump itself, or I can get to drilling one of my spare nozzles. What would you guys recommend? A .005 increase?
I can tell you guys that when I replaced the stock nozzle with a .043, it went from falling on it's face (could get it to die actually if not careful) to "OMG, this is really drivable and intermittent now, and when it does happen it's far more mild". So going bigger was definitely a positive change. Sounds like I could probably go even bigger.
Try: Check your base timing and advance it 3 or 4 degrees, reset your idle speed and see what happens to the flat spot. Easy to do.
Late to the party on that one!
My advance is maximized before ping with a re-curved dizzy.
I have a .0465" jewler's bit. I have a bunch of bits in the mid .05 range, but I feel that's too much of a step up....
That is a wicked stumble. Try lowering the pump stem. You may have the wrong plunger as stated earlier. Make sure the secondary air door is not floppy loose-this will effect tip-in if it's super loose. Drilling is a last resort in my opinion.
The pump came in K4084 (MIke's Carb Kit). It looks to be correct?
https://www.carburetor-parts.com/Carter-AVS-Carburetor-Kit--69-71-Chrysler-Plymouth_p_653.html
The air door isn't overly floppy or anything like that. It does have some tension. That was set by the book and not-touched sense.
Keep in mind, I would be drilling a spare edel tip that I would never otherwise use, so there's no "oops" risk on that one.
I have the air horn off now. Floats confirmed to be correct.
Considering to drill my spare (edelbrock) nozzle to .0465 and throw it on. It's a small step increase.
If you thought that stumble was wicked, you should have saw it with the .033 nozzle.....
Not sure on the kit. quadrajetparts.com has photos and detailed info on dimensions. I would check this first.
https://quadrajetparts.com/accelerator-pumps-c-299_130_131.html
Since you have the top off you can measure the pump plunger
Quote from: bennydodge on February 29, 2020, 04:19:20 PM
Not sure on the kit. quadrajetparts.com has photos and detailed info on dimensions. I would check this first.
https://quadrajetparts.com/accelerator-pumps-c-299_130_131.html
Since you have the top off you can measure the pump plunger
:iagree: You may have some mis-matched parts there and drilling the squirter out is just compensating for and error elsewhere. Check out the carb component part numbers carefully to verify the correct application. :alan2cents:
2.2" long....
I would drill the squirter :alan2cents:
My Carter is 4937S.
So it would be this one:
https://quadrajetparts.com/accelerator-pump-plunger-1316-leather-length-p-859.html
What is should measure:
Over all length (OAL): 2.27"
Pump Cup diameter: .81"
Stem Length 0.900" (length above from spring retainer to stem tip)
Cup Style: Leather
What mine measures:
Over all length (OAL): 2.25"
Pump Cup diameter: .80"
Stem Length 0.900" (length above from spring retainer to stem tip)
Cup Style: Leather
I believe that my accelerator pump is correct.
Quote from: Chryco Psycho on February 29, 2020, 04:46:29 PM
I would drill the squirter :alan2cents:
I drilled my spare Edelbrock .021" squirter to .046". If I had a .048" bit I would have done it, but .043 to .046 is probably a decent step for the time being.
Reassembling now.
Yes, it appears you have the right plunger. Maybe lower the pump stem slighty...If that doesn't work I would drill the squirter or get a larger one-certainly easier to drill one out. Do you have the stock squirter on it now? Stock AVS pump clusters are different than the Eddy's.
You say you have am OEM 750 AVS? You could also swap the 750 squirter on to the 625. I'm not sure but I think the 750 pump shooter is .043
Long shot here, excessive slack in the throttle cable. I suppose lots of slack could create the "sensation" of a hesitation.
Update:
I need to drive more to assess, but from a stand-still it is responsive. No hesitation.
When cruising, I now get a hesitation by pressing the pedal halfway down quickly from cruising "blurp blurp then go"
I have 4 squirters:
1) OEM, which is probably. .033.
2) Edelbrock .021 (which is now .046 and is installed)
3) Edelbrock .033
4) Edelbrock .043 (which was installed prior)
The Edelbrocks will fit if you grind off the backside to delete the rear bolt hole.
I'm thinking to return the linkage to the second position and reset the plunger height. Then fine tune from there....
Unless my issue is now something else.
Quote from: kawahonda on February 29, 2020, 05:55:17 PM
Update:
I need to drive more to assess, but from a stand-still it is responsive. No hesitation.
When cruising, I now get a hesitation by pressing the pedal halfway down quickly from cruising "blurp blurp then go"
I have 4 squirters:
1) OEM, which is probably. .033.
2) Edelbrock .021 (which is now .046 and is installed)
3) Edelbrock .033
4) Edelbrock .043 (which was installed prior)
The Edelbrocks will fit if you grind off the backside to delete the rear bolt hole.
I'm thinking to return the linkage to the second position and reset the plunger height. Then fine tune from there....
Unless my issue is now something else.
The fact that a bigger squirter helps means you are on the right path , it would seem the next drill size is where you need to be to get rid of the 1/2 throttle hesitation with quick opening while cruising
Progress indeed. Sounds like the secondary air door needs tightening now.
or 1 step richer in cruise jetting
The problem though is that the hesitation during cruise is a new thing--it didn't used to do that. I solved the problem down low but moved a new problem towards the middle.
I'll speak on it some more when I drive it tomorrow to really get a good assessment. After she was good and warm, she just speed off like normal from a complete stop with "decent" pedal movement every time I tried it.
I'll check the metering rods/pistons closely tomorrow....sometimes you can install the caps incorrectly where they are not fully "flat" seated.
Progress indeed!
Quote from: kawahonda on February 29, 2020, 04:58:35 PM
My Carter is 4937S.
So it would be this one:
https://quadrajetparts.com/accelerator-pump-plunger-1316-leather-length-p-859.html
What is should measure:
Over all length (OAL): 2.27"
Pump Cup diameter: .81"
Stem Length 0.900" (length above from spring retainer to stem tip)
Cup Style: Leather
What mine measures:
Over all length (OAL): 2.25"
Pump Cup diameter: .80"
Stem Length 0.900" (length above from spring retainer to stem tip)
Cup Style: Leather
I believe that my accelerator pump is correct.
Nice job on the research! Good to know that you have the correct components to work out these situations. Carb tuning will generally move the flat spot upwards in the fuel circuits until solved from what I've experienced. Question; Are you running ethanol blended fuel or ethanol free? It makes a difference in the tune unfortunately.
Sounds like if I can CONFIRM that hesitation NEVER happens again from a stop-go at "adequate" throttle (not flooring it, or even halfway flooring it), but a nice "go" effort, then we can assume my accelerator pump is doing precisely what it need to be doing, and time to move on to other sections?
1) Air door tightening
2) Richen cruise jetting (is this primary or secondary)
3) Does metering rod assembles play into this? Correct me if I'm wrong, but metering rods are not part of the transition circuit. It's likely that those won't need to be touched.
Sounds like I may not need to bother playing with the pump anymore if I'm reading everyone correctly. My instinct WAS to lean it by changing the pump arm position back to the middle and reset the pump height and to reassess. If this is a wasted effort, let me know!
I wrote my jet sizes down somewhere...maybe if you guys are all aligned I should be upping my cruise jetting let me know and I can post whatever they are....maybe someone around here has some laying around. :)
I'm running ethanol blended fuel, 91 octane. I can run ethanol free, but it's a pain in the arse to find 91+....basically means I need to drive 9 miles out of the way (one way) to refuel. I had my dizzy re-curved based on 91 blended. Heads are "J" heads and likely have hardened seats. No point now to keep with an ethanol free blend...should just plan on running blended fuel in this baby at this point...
Crycho...you've seen my plugs in other threads....I think you mentioned they are just about perfect..."maybe 1 jet up" is what I think you posted.
Stock jetting for a 4937S
primary jet- .089 (120-489)
metering rod- .065/.064/.055 (16-574)
secondary jet- .096 (120-396)
In my experience going to a thinner metering rod(at least on the mid and power steps) has always picked up a noticeable performance increase on the small factory AVS. Even with a stock engine.
1) Air door tightening - Secondary circuit, hard throttle acceleration. Loose spring tension will cause a bog when the secondaries open.
2) Richen cruise jetting (is this primary or secondary) -Cruise jetting is on the primary side. AVS uses metering rod/jet combination and calibrated springs.
3) Does metering rod assembles play into this? Correct me if I'm wrong, but metering rods are not part of the transition circuit. It's likely that those won't need to be touched. - The metering rod/jet/calibrated springs come into play on all circuits somewhat. The idle fuel quantity is trimmed with the mixture screws. The jet ID is larger than the OD of the metering rod allowing metered fuel to flow past. The stock size rod has 3 steps; .065", .064" and .055" and run in a .089" jet. A set of smaller OD metering rods (or larger jets) should richen the mixture. Metering rods are easier to change than the jets. Ethanol blended fuel will make the engine run lean with stock jet/metering rod combination, as will a free flowing exhaust, open air cleaner etc. As bennydodge pointed out, most of the cars where jetted lean to begin with back in the day. Also be sure to use Stabil for ethanol or similar in your fuel to prevent corrosion from plugging up the fuel circuits in the carb. :alan2cents:
Yes, metering rods do make a difference as do step up springs. You could run the first step of the rod factory-sized but make the mid and power steps smaller and this would make the transition smoother. Stock step-up springs are rated at 10" which should be fine for stock/stockish engines.
The OP's carb is an ECS carb, I think this stands for evaporative control system??- also referred to as a "California" carb. The non-ECS 340 carbs have richer secondary jetting and slightly different metering rods.
I'd try Air door tightening. Had a similar transition bog from my 625 Holley Demon. Thought I was doing something wrong but kept going 1/4 turn at a wack. Took nearly 2 full turns to get the spring tight enough, bog is officially gone.
My2c.
Quote from: Scooter on March 01, 2020, 09:19:51 AM
I'd try Air door tightening. Had a similar transition bog from my 625 Holley Demon. Thought I was doing something wrong but kept going 1/4 turn at a wack. Took nearly 2 full turns to get the spring tight enough, bog is officially gone.
My2c.
Damn, 2 full turns... Either the door was super loose out of the box or the secondary jetting is to lean. :alan2cents:Those Street Demons are nice , I've got the 750 cfm phenolic float bowl model-pretty good carb
^^^ Been pretty satisfied with mine once adjusted properly, think it was just loose from the factory. Got the phenolic float bowl hoping it would help with my CA blend gas burning off in the bowl after shutdown.. did not make a difference. Car never runs over 180(big alum rad and switched fans), when I shut it down you can pop the hood and hear the fuel boiling in the carb. Might see if I can get a non metallic spacer in there this summer.. not much hood clearance tho.
Sounds like OP has very similar air door bog issues. Trying the adjustment first is 0 cost, that's where I started after making the initial idle adjustments with a vac gauge. Took about 30 minutes to get mine adjusted properly. Just kept running up and down the highway from one exit to the next rolling on the throttle. Get out.. pop hood, turn screw1/4 counterclock. Rinse, wash, repeat.
GL OP
-Scoot
Quote from: bennydodge on March 01, 2020, 09:19:27 AM
Yes, metering rods do make a difference as do step up springs. You could run the first step of the rod factory-sized but make the mid and power steps smaller and this would make the transition smoother. Stock step-up springs are rated at 10" which should be fine for stock/stockish engines.
The OP's carb is an ECS carb, I think this stands for evaporative control system??- also referred to as a "California" carb. The non-ECS 340 carbs have richer secondary jetting and slightly different metering rods.
:iagree: Evaporative Control System carb for CA requirements in 1970. Jetted lean from the factory can be expected. 3 step AVS metering rods appear to be scarce, might have to try 2 step rods.
My jets are:
Front 489
Rear 120
Quote from: kawahonda on March 01, 2020, 10:14:05 AM
My jets are:
Front 489
Rear 120
You should see a "120" and a "396" stamped around the top of the jet-I've seen factory carbs that are missing the size stamp. 120 is stamped on one side of the jet and 396 should be stamped on the opposite side. Your metering rods should also be stamped "16-574".
Those are the sizes I recorded when I rebuilt the carb...
I'm driving it now. I would say that I made it worse from where it was.
I don't think we need to worry about the air door yet. Down low it's worse.
I'm going to put the linkage back to the center and reset the plunger height. Reassess then.
I may cheat and just install the square bore AVS. Gain a few ponies too. :)
Going to do another stop-go test ride. May make another video.
The FSM claims Carter AVS #4937S is equipped with a hot idle compensator valve. Do you still have this valve in place and check that it is sealing? https://www.allpar.com/photos/mopar/carburetor/carter/hot-idle-compensator.jpg Just a thought.
Yea, that valve is in place. Not sure how to test if it's "sealing" though.
I drove it today some more and its works pretty good. I went over to my engine builder's house and had him drive it. We went on a 4 mile run, and that "hesitation" happened twice--much more often that it "didn't happen.
He thinks it has nothing to do with the squirter size. He was able to get it to do that while "barely" pushing on the pedal by accident. It has no carb hesitation at all from cruise. I think I said that it did yesterday because it probably wasn't fully up to normal engine temperature.
We both agreed that it is "minor" and no one should be losing sleep over it. He said he would just drive it and not tinker with it.
He mentioned if I wanted to toy with it, then I should set the floats higher (use a smaller bit). Basically, the idea is to go as high as you can before it leaks. If you can picture the "float", there is a "seam" in the center on the top side. Do you guys incorporate that "seam" when sliding a drill bit behind it, or do you keep the drill bit on the bulk of the top surface (and ignore the protruded "seam")? If my floats are set accordingly, is there a recommended "next size" drill bit to try?
He also said that I should back my timing off. I'm at 15 initial now. I may try 13 or 14 initial. It's basically right on the cusp of being a little too much. If it's just me driving and if I "get on it" I don't get any pinging. But with me and him in the car (more load), you can then get some faint pinging noise if you stress the engine. So I'll lower the timing a tad bit (probably drop it one degree) and reset everything. Then proceed to maybe alter the floats a little bit...
Of course I can "drive" it to where it won't do this, but this is another video showing the stumble (me purposely trying to do it). The first stumble was pretty bad that you'll see. You'll see the others are very mild. There was a couple times where it didn't do it.
This video is .046 squirter in the most "rich" part of the lever. I would say that going from .043 to .046 did not create any "for sure" change.
1) Reduce float height
2) continue to "up" the squieter size, try .050.
Maybe this is not squirter related. The video above I was pressing the throttle 10% and not being very aggressive. Definitely nothing to do with secondary door.
With the air horn inverted and gasket in place, use a 7/32" drill bit or gauge between the top of the float seam (in the front) and the gasket. Use a smaller drill bit to raise the level. Check the float drop and alignment as well. The specs are in the '70 FSM pages 551-552 or 14-124 and 14-125.
With a 7/32 bit rolling underneath the float (including that thicker "seam" part and gasket in place) the float will move slightly. So it's actually set slightly smaller than 7/32...
Quote from: kawahonda on March 01, 2020, 04:23:45 PM
With a 7/32 bit rolling underneath the float (including that thicker "seam" part and gasket in place) the float will move slightly. So it's actually set slightly smaller than 7/32...
Slight contact is fine, not an exact science here. Remember this is liquid fuel and its sloshing around like mad when driving. Imagine the action in a full cup of coffee on the hood. You might want to invest in a quality AFR gauge at this point. It's a real time saver in carb tuning. The secondary air door adjustment is in the FSM. 2 turns from wide open, I would go a little tighter until you get the primary side figured out. :alan2cents:
Quote: Yea, that valve is in place. Not sure how to test if it's "sealing" though.
The hot idle compensator is a bi metal leaf that should normally seal a vacuum port drilled through the carb body. Pushing down the leaf should not change the engine rpm if it is closed already. There shouldn't be any movement in the closed valve either. If this thing is sticking open at random or opening at a low temp, tuning will be impossible. Its worth looking at, I would plug the port. :alan2cents:
If this is the thing that leads to that "larger" exterior port on the left side, then yep, there is a plug on her already. :)
I'm wondering if my jetting is just a bit too lean to begin with. I wonder if this has nothing to do with the accelerator pump. I would think that the pump "tuning" would come more into play for "quick' transitions when the pedal really moves, not for slow (but "purposeful") 10% foot movements.
Again, I'm no expert. But a .046 bored nozzle is getting pretty damn up there--it's larger than Edelbrock's largest nozzle that they sell @ .043. My engine is only a 340, it ain't a big block.
Is it common that people go even larger as one way to solve this?
I would love to see what AFR my rig is pulling. If I ever went that route, I'd go for a temp install. It isn't cost-effective for a temp install.
Quote from: kawahonda on March 01, 2020, 05:08:04 PM
If this is the thing that leads to that "larger" exterior port on the left side, then yep, there is a plug on her already. :)
I'm wondering if my jetting is just a bit too lean to begin with. I wonder if this has nothing to do with the accelerator pump. I would think that the pump "tuning" would come more into play for "quick' transitions when the pedal really moves, not for slow (but "purposeful") 10% foot movements.
Again, I'm no expert. But a .046 bored nozzle is getting pretty damn up there--it's larger than Edelbrock's largest nozzle that they sell @ .043. My engine is only a 340, it ain't a big block.
Is it common that people go even larger as one way to solve this?
I would love to see what AFR my rig is pulling. If I ever went that route, I'd go for a temp install. It isn't cost-effective for a temp install.
The hot idle compensator valve is in between the secondary venturies, where a secondary acellerator pump nozzle would go. It kind of looks like a feeler gauge blade. The part on the left side you mention is probably the bowl vent valve, part of the ECS.
Your on target with the acellerator pump theory. It only pumps fuel when you advance the throttle and not in a "steady state" as you've noticed. The metering rods/jets/spring combination takes care of steady state fueling. The engine may be burning off the pump shot and then falls off due to lean condition. You can drill the nozzles out some more but I think you have hit the point where the engine is getting all of the fuel the acellerator pump has to deliver.
Here is an Amazon link to a stand alone AFR gauge that may be of interest:
https://www.amazon.com/Innovate-Motorsports-BASIC-Digital-Wideband/dp/B001S7W836/ref=pd_sbs_263_1/138-4682770-8667205?_encoding=UTF8&pd_rd_i=B001S7W836&pd_rd_r=0fc16d81-773c-4a2f-ae92-290caf89e590&pd_rd_w=xGqa9&pd_rd_wg=PUEnJ&pf_rd_p=7cd8f929-4345-4bf2-a554-7d7588b3dd5f&pf_rd_r=VEB9AGCYSCDJ382EN7M3&psc=1&refRID=VEB9AGCYSCDJ382EN7M3
Here are my plugs
Looks like its running lean to me. The plugs should be tan not white. White means the plugs are running hot which can cause the pinging under load.
If I "jet up", could I run into the case where I could actually get away with more advance? Seems logical if so....my dizzy recurver set mine up to run on 91 blended fuel and 15-17 initial advance! I'm back down to 13 advance to keep it from pinging at full load with passengers in the car...
That might just be the final key to this puzzle...it's running lean, and it probably isn't a accell pump thing...
What's the next jet size that I should try? Figure going one step up would be good. What do you guys think?
Current jets: Front 489, Rear: 120.
Could use some help to figure out what to get next. In my opinion, all signs are pointing towards to jet up a level....
My research tells me that:
Primary 489: .089" - confirmed
Secondary: uknown, my dad only wrote "120" which doesn't tell me anything
Metering rods: 16-574 (.065 x .060 x .053)
I do have a spare AFB that I can use to convert to Edelbrock stuff (requires new metering rods and jets and flat covers. I don't want to put TOO much time/money/effort into this carb because the engine will be replaced soon, but I'd like to keep it all as an assembly with the right tuned OEM carb to go with it. Let me know what all I should do here.
Perhaps my AFB, if the jets are interchangable, may have some jets that I could use, if AFB and AVS jets are interchangeable?
As always, double-check my work/research.
This is another issue with AFB / AVS carbs , up jetting is not simple , Yes the jets interchange BTW
You need to change a combination of jets & metering rods to step up 1 size & them the metering rods cange change 2 areas such as criuse & WOT when you only want to change 1 of the 2
Holley is easier as you can just change the jet for one that is a .001 bigger with no effect on any other circuit .
Anyway , you could just drill the jet .001 -.002 if you have the right drill bits
I just removed my jets/metering rods from my chevy AFB.
Front (main): 120-400, which tells me it's 1.00.
Rear: can't tell, but it looks like 120- X95, where "X' is hard to make out. It's probably a .095 jet.
Metering rods are 16-W8500, 3-step rods. From a corvette forum, this shows as .0725 x .0470
At least that's what I have on hands now, at least.
Not sure if I should use any of it, or parts of it. Tell me what to do. I'd rather buy a couple jets or a set of rods if that's all I need. Sounds like I need to pull my rods and figure out what they are.
do you have a caliper handy ? if the rods are thinner try them
Go your PM. Thanks Crycho.
Let me get the airhorn off of the 4937s carb first, just so I can accurately say what jets I have. I confirmed the primary and the metering rods already, but the secondaries I need to check because my father just wrote "120", which is not the size (just the first few digits).
I texted my engine builder about this idea of jetting up 1 level, and he responded "or 2 levels". :)
What I absolutely have no idea on is how to "jet up" to solve my issue. Not sure if I should be focusing on mains, secondaries, or rods, or all 3. That's where I'll look towards your guy's expert opinion.
I'll probably start tomorrow on getting the air horn off (again). :)
At least I got the AFB dissembled. Who knows, maybe there's something to use from it, maybe it's way off.
I would richen the primaries first so thinner rods or larger jets , usually a combo of both to move 1 size
Interesting.
Looking at this Carter page:
https://board.moparts.org/ubbthreads/ubbthreads.php/ubb/download/Number/170980/filename/8258711-Metering_rod_and_jet_sizes.jpg
My metering rod is listed (16-574) @ .065 x .064 x .055.
My main jet is listed in the "AFBS-AVS Primary High Step Jet for staged metering (Not interchangable w/ low step jets)". Not sure what this means, but it's listed there as 120-489 @ .089. Is that just a fancy word for 3-stage rods? Seems like there's only 3 "compatible" jets listed there.
Anyhow, let me know what part #s you would recommend by looking at that. I can ring you tomorrow as well.
EDIT, the mains and metering rods are not interchangeable between the AFB that I have. The AFB that I have uses 2-step metering rods, which has the "shorter" jet height and the "flat top" covers. The secondaries are probably the only thing I can use from it, or use the flat top covers and get edelbrock kit, but I'll try to avoid that for the time being. :)
This is an ECS "California" Carb. Curious what the non ECS 340 carbs used. That may be the reference point.
Here's a set of rods on fleabay. (.065 x .062 x .053) in sexy carter packaging. That will richen stage 1 and 2 by a couple notches. Snab it? Or is this too minimal...
https://www.ebay.com/itm/PAIR-OF-CARTER-AFB-AVS-CARBURETOR-THREE-STEP-METERING-RODS-065-053-062/402061352591?hash=item5d9cb95e8f:g:P1gAAOSwoXRZjdSu
There are others available on eBay as well that are smaller. Let me know if I need to jump on any of them.
That was the Carter info I was looking for! As you can see, there aren't many 3 step metering rods available anymore, I would get the eBay sets just to have on hand. There are 2 sets you could try: ,065x.062x.053 and .063x.060x.051. That's your one and two step increase suggested. If you look at the Edelbrock website for Thunder AVS carb in 650 cfm you'll see the out of the box jet/rod/spring setup. .095 primary jet with .065x.047 metering rod equals .030"/.048 rod to jet clearance. Uses 5 InHg springs. You have .089 jet with .065x.064x.055 m rod so that's .024x.025 x.034" rod to jet clearance by comparison. Not exactly the same carb but a significant difference in clearance.
https://www.edelbrock.com/thunder-series-avs-650-cfm-off-road-carb-with-manual-choke-in-satin-non-egr-1825.html
If you are going to take the carb apart I would check the idle fuel jets on the bottom of the boosters. The FSM states .031" stock jet size, maybe increase it to .033" or so and trim off with the mixture screws. :alan2cents:
Quote from: Chryco Psycho on March 01, 2020, 08:07:35 PM
This is another issue with AFB / AVS carbs , up jetting is not simple , Yes the jets interchange BTW
You need to change a combination of jets & metering rods to step up 1 size & them the metering rods cange change 2 areas such as criuse & WOT when you only want to change 1 of the 2
Holley is easier as you can just change the jet for one that is a .001 bigger with no effect on any other circuit .
Anyway , you could just drill the jet .001 -.002 if you have the right drill bits
Yeah, we get it, you love Holleys, blah blah blah...How the hell does this help the OP?? What's hard about changing a set of metering rods?? It literally takes 1 minute to do and no messy gas spills. It's also very EASY to understand. The thinner the rod the more fuel flows through the jet. If you need to, take a few extra minutes and take the top off for a jet change. This is not rocket science... Anyway....
1970 Carter AVS 4934S no ECS
Primary jet-.089 (120-489)
Metering rod-.066/.064/.055 (16-546)
Secondary jet-.098 (120-398)
Going richer might solve your issues. You probably know this already but the factory Carter AVS primary jets are a different(high step) design than standard AFB jets. If you change to AFB/Eddy jets you will have to run all Eddy/AFB stuff in the primary side: metering rods, metering rod covers, jets.
Based on your plug reading I would go a little richer on the jets/rods.
Perfect, I'll grab them both.
Not sure if I'll take the carb apart quite yet. Eventually. If I can solve this "cruise mode" lean spot with a metering rod change, then it's time to actually dial back on the accelerator pump. Probably will put the .043" one back in and reset it to the center pivot. Once that's set, I may consider advancing my timing again by a degree or two.
Interesting note about the additional idle fuel jets--I'll maybe look into that. Is that a strong recommendation?
Wouldn't only changing out metering rods still require trimming on the mixture screws?
Thanks Bennydodge for that info. Looks like the No-ECS is the same jetting with a slightly thicker top portion meter. No evidence so far that the ECS models were "leaned out".
Is it true that Carter only produces 3 "tall" jets for the 3-step roads?
Edit: Sounds like a good plan is to remove air horn and identify secondary jet. Jet up to .098.
Quote from: kawahonda on March 01, 2020, 09:59:07 PM
Interesting.
Looking at this Carter page:
https://board.moparts.org/ubbthreads/ubbthreads.php/ubb/download/Number/170980/filename/8258711-Metering_rod_and_jet_sizes.jpg
My metering rod is listed (16-574) @ .065 x .064 x .055.
My main jet is listed in the "AFBS-AVS Primary High Step Jet for staged metering (Not interchangable w/ low step jets)". Not sure what this means, but it's listed there as 120-489 @ .089. Is that just a fancy word for 3-stage rods? Seems like there's only 3 "compatible" jets listed there.
Anyhow, let me know what part #s you would recommend by looking at that. I can ring you tomorrow as well.
EDIT, the mains and metering rods are not interchangeable between the AFB that I have. The AFB that I have uses 2-step metering rods, which has the "shorter" jet height and the "flat top" covers. The secondaries are probably the only thing I can use from it, or use the flat top covers and get edelbrock kit, but I'll try to avoid that for the time being. :)
This is an ECS "California" Carb. Curious what the non ECS 340 carbs used. That may be the reference point.
Here's a set of rods on fleabay. (.065 x .062 x .053) in sexy carter packaging. That will richen stage 1 and 2 by a couple notches. Snab it? Or is this too minimal...
https://www.ebay.com/itm/PAIR-OF-CARTER-AFB-AVS-CARBURETOR-THREE-STEP-METERING-RODS-065-053-062/402061352591?hash=item5d9cb95e8f:g:P1gAAOSwoXRZjdSu
There are others available on eBay as well that are smaller. Let me know if I need to jump on any of them.
Those metering rods, if they are that size (.065/.062/.053) are good. Jet up on the secondary to .098 as well.
Quote from: kawahonda on March 02, 2020, 07:48:34 AM
Perfect, I'll grab them both.
Not sure if I'll take the carb apart quite yet. Eventually. If I can solve this "cruise mode" lean spot with a metering rod change, then it's time to actually dial back on the accelerator pump. Probably will put the .043" one back in and reset it to the center pivot. Once that's set, I may consider advancing my timing again by a degree or two.
Interesting note about the additional idle fuel jets--I'll maybe look into that. Is that a strong recommendation?
Wouldn't only changing out metering rods still require trimming on the mixture screws?
Thanks Bennydodge for that info. Looks like the No-ECS is the same jetting with a slightly thicker top portion meter. No evidence so far that the ECS models were "leaned out".
Is it true that Carter only produces 3 "tall" jets for the 3-step roads?
Yes, I believe there's only 3 high step jets .089,.098,.101. My 1970's AVS strip kit has those 3 sizes only, but there are 4 different sized metering rods and a multitude of secondary jets.
The non ECS carbs are richer but only in the secondary side. I can't verify if the ECS carbs have air bleeds and fuel restrictors that are leaner but it stands to reason they would be.
Edit: Sounds like a good plan is to remove air horn and identify secondary jet. Jet up to .098.
Sorry, my response got mixed up in the middle of you last response... :pullinghair:
One recommendation I can make that helped me a bunch was getting a FACTORY service manual. Nice section on AVS's in there.
Some good reading/reference material here-April 1990 Mopar Action. Hopefully you can blow this up and read it.
Not sure why these pics rotated on me..
Fantastic material there. That's stuff you can't even find online. I'm saving that for sure.
Now I'm excited to remove my air horn to see what secondary jet sizes I have. It should be .098.
Yep, I got the FSM and also a carb/edel tune book.
Quote: Perfect, I'll grab them both.
Not sure if I'll take the carb apart quite yet. Eventually. If I can solve this "cruise mode" lean spot with a metering rod change, then it's time to actually dial back on the accelerator pump. Probably will put the .043" one back in and reset it to the center pivot. Once that's set, I may consider advancing my timing again by a degree or two.
Great Idea!
Interesting note about the additional idle fuel jets--I'll maybe look into that. Is that a strong recommendation?
- Yes, Very Strong. Most of the carb issues I see are caused by dirt etc plugging things up. The idle passages are most effected due to the small size (.031" in this case). I would drill the idle jets out a few thousandths and readjust the mixture screws, just don't over do it. They should be evenly synchronized in a perfect world. You should be able to have full adjustability from too rich, at say 3 turns and too lean, at say 1 turn out (+-) Perfect at, say 2 turns. Now you will know that the idle circuit can provide more than enough fuel than needed. Check your hot idle compensator or plug the passage. Its probably original 50 yrs old...
Wouldn't only changing out metering rods still require trimming on the mixture screws?
- Possibly but very slight, the idle jets are in play here.
Thanks Bennydodge for that info. Looks like the No-ECS is the same jetting with a slightly thicker top portion meter. No evidence so far that the ECS models were "leaned out".
-Great Info! Both carbs were likely "leaned to the max" to meet emissions. Fuel was much different formula back then also.
Is it true that Carter only produces 3 "tall" jets for the 3-step roads?
- Edelbrock bought Carter years ago and use AFB 2 step rods and jets on their AFB/AVS series. No listing for tall jets or 3 step rods on their site. It appears there were only 3 tall jets available from Carter. You could ask Uscarburetors if you're getting the 3 step rods from them. Old school place!
Unless it's a misprint you should have .096 size in the secondary.
Quote from: bennydodge on March 02, 2020, 08:38:04 AM
One recommendation I can make that helped me a bunch was getting a FACTORY service manual. Nice section on AVS's in there.
There is a 70 FSM available for download on this site under the "Resources" tab. That's where I found it. :bigthumb:
Benny- yep, I was just eyeballing exactly that!
Sounds like a .098 move is a definite.
Where do I find this idle jet online, contact usecarbs?
Quote from: kawahonda on March 02, 2020, 08:57:50 AM
Benny- yep, I was just eyeballing exactly that!
Sounds like a .098 move is a definite.
Where do I find this idle jet online, contact usecarbs?
You can ask UScarburetor about AVS Tall Jets, the idle jets are part of the primary boosters in your carb already.
Quote from: 734406PK on March 02, 2020, 09:15:40 AM
Quote from: kawahonda on March 02, 2020, 08:57:50 AM
Benny- yep, I was just eyeballing exactly that!
Sounds like a .098 move is a definite.
Where do I find this idle jet online, contact usecarbs?
You can ask UScarburetor about AVS Tall Jets, the idle jets are part of the primary boosters in your carb already.
Nice photo there. I think he's referring to the main secondary jets. These would be standard AFB/Edelbrock stuff.
So I should inquire about boosters that have the larger jet installed since its kind of a one piece ordeal. I don't see a lot on eBay, and without a part # is it going to be anyone's guess as to what size the built-in jet is?
Question here: Are they all .031, or are certain carters .033?
Another question: Are the AFB boosters interchangeable with the AVS? Probably not.
I'd hate to drill out my originals here...would rather get another set that has the correct size, or to drill a "spare" set.
If they are all .031", then it's probably best to attack this last and only if needed. That's my thinking.
I'll definitely ask/obtain about the .098 jet.
I don't think I'll need to mess with the main jet for now since I have two needle sizes to try on the way!
Quote from: kawahonda on March 02, 2020, 09:44:48 AM
So I should inquire about boosters that have the larger jet installed since its kind of a one piece ordeal. I don't see a lot on eBay, and without a part # is it going to be anyone's guess as to what size the built-in jet is?
Question here: Are they all .031, or are certain carters .033?
Another question: Are the AFB boosters interchangeable with the AVS? Probably not.
I'd hate to drill out my originals here...would rather get another set that has the correct size, or to drill a "spare" set.
If they are all .031", then it's probably best to attack this last and only if needed. That's my thinking.
I'll definitely ask/obtain about the .098 jet.
I don't think I'll need to mess with the main jet for now since I have two needle sizes to try on the way!
Trying to find a pair .033" boosters is going to be tough without a part number IMO. The idle jet size,air bleed etc will be application specific but ask Uscarburetor, you never know...
The idle jets can be filled/crimped and drilled back out to.031" if needed but i doubt you will have to do that, you have plenty of adjustment in the idle mixture screws.
If you zoom in on the second photo that bennydodge posted, there is a Carter suggested carb tune for a modified 340, pretty interesting, staggered jetting. :bigthumb:
Quote from: kawahonda on March 02, 2020, 09:44:48 AM
So I should inquire about boosters that have the larger jet installed since its kind of a one piece ordeal. I don't see a lot on eBay, and without a part # is it going to be anyone's guess as to what size the built-in jet is?
Question here: Are they all .031, or are certain carters .033?
Another question: Are the AFB boosters interchangeable with the AVS? Probably not.
I'd hate to drill out my originals here...would rather get another set that has the correct size, or to drill a "spare" set.
If they are all .031", then it's probably best to attack this last and only if needed. That's my thinking.
I’ll definitely ask/obtain about the .098 jet.
I don't think I'll need to mess with the main jet for now since I have two needle sizes to try on the way!
I can't definitively answer any of these questions but I wonder if the emulsion in the booster clusters is different between Federal and ECS carbs-idle jets and air bleeds being different. Never measured any of them. I don't know of anybody selling or modifying AVS booster clusters.
Modern fuel has less energy(BTU's) than older fuel and, of course, these old carbs were calibrated using the older fuel. This means that stock calibrations of old carbs are going be even leaner than back in the old days. So if it were mine I would get the jetting closer to optimal(richer) before I did anything else.. :alan2cents:
You guys rule. Really love the help. Over the past 24 hours, I've learned a hell of a lot about these so far!
That is an interesting staggered setup...both in the rods and in the jets. That's kinda going in a little deeper than what I'd like to do, at least for the time being. :)
Thanks for continuing along on my journey. I'm pretty sure I'm going to solve this real soon!
I'm kinda thinking in the future, but it seems like the accelerator pump gets blamed for a lot of things when many times it's probably not the issue. I wonder if my .043 and .046 have really just be compensating for this lean issue all along...wondering if I may even put back the factory .033 squirter (eventually).
You should always do one thing at a time, but I'm going to break that rule in this case. Removing air horn today.
1) Will replace secondary jets from .096 to .098. This is the spec for non-ECS carbs.
2) Will put install "large" accelerator nozzle (.043) from the "extra large" (.046) that is on there right now.
3) Considering to replace the boosters with larger ones, or may just "drill".
4) How to test that metallic piece that is in there for proper sealing?
Retune/retry carb. Likely issue will be fixed. Position back pump to center position and recheck. If no change in the transition part, then keep it there.
Then move to advance timing back up and see if I've unlocked some new potential there.
At this point if all is well, you can consider carb tuning done. But knowing me, I just "may" go back to the .033 pump if I remove the air horn again and retest. I don't think there's anything wrong with leaving the .043 on there if not needed. Probably slightly worse fuel economy?
Tuning is fun.
BTW, UScarb doesn't have the larger boosters. So my only option is to drill. I'm still kinda "iffy" on that. That graphic you posted shows that it will help with my issue, so kinda makes me want to try it.
I would take it off and plug the passage. :alan2cents: There is another 4937S for sale on eBay. I did find the Mopar part numbers for the boosters but no luck on a web search. 3514889 and 3514888. Drilling jets is considered taboo by many,but as time goes on its the only choice sometimes. Also the idle jet is responsible for fuel metering in the transition slot just above idle, but make a jet/rod change first and drill out the idle jet as a last resort.
To much pump shot is actually a bad thing=sluggish throttle response and tip-in. You want it as lean as possible without a stumble or bog, this will make response crisper and snappier.
You know I've never had problems with the hot idle compensator-even on big cam engines. It's designed to increase idle speed and therefore help cool the engine under certain conditions. The port under the strip goes straight to manifold vacuum-essentially a controlled vacuum leak. It should only open under extreme heat conditions, such as A/C on, 100 degree temps, stop and go traffic-all 3 of these things at once could make it open. I've seen guys fashion block off plates to get rid of this device. I guess if it fails in the "open" position it would be problematic.
Quote from: 734406PK on March 02, 2020, 10:10:23 AM
Quote from: kawahonda on March 02, 2020, 09:44:48 AM
So I should inquire about boosters that have the larger jet installed since its kind of a one piece ordeal. I don't see a lot on eBay, and without a part # is it going to be anyone's guess as to what size the built-in jet is?
Question here: Are they all .031, or are certain carters .033?
Another question: Are the AFB boosters interchangeable with the AVS? Probably not.
I'd hate to drill out my originals here...would rather get another set that has the correct size, or to drill a "spare" set.
If they are all .031", then it's probably best to attack this last and only if needed. That's my thinking.
I'll definitely ask/obtain about the .098 jet.
I don't think I'll need to mess with the main jet for now since I have two needle sizes to try on the way!
Trying to find a pair .033" boosters is going to be tough without a part number IMO. The idle jet size,air bleed etc will be application specific but ask Uscarburetor, you never know...
The idle jets can be filled/crimped and drilled back out to.031" if needed but i doubt you will have to do that, you have plenty of adjustment in the idle mixture screws.
If you zoom in on the second photo that bennydodge posted, there is a Carter suggested carb tune for a modified 340, pretty interesting, staggered jetting. :bigthumb:
I noticed the staggered deal as well-and those guys really tested this stuff back then, sharp dudes for sure...
Quote from: bennydodge on March 02, 2020, 11:22:09 AM
To much pump shot is actually a bad thing=sluggish throttle response and tip-in. You want it as lean as possible without a stumble or bog, this will make response crisper and snappier.
You know I've never had problems with the hot idle compensator-even on big cam engines. It's designed to increase idle speed and therefore help cool the engine under certain conditions. The port under the strip goes straight to manifold vacuum-essentially a controlled vacuum leak. It should only open under extreme heat conditions, such as A/C on, 100 degree temps, stop and go traffic-all 3 of these things at once could make it open. I've seen guys fashion block off plates to get rid of this device. I guess if it fails in the "open" position it would be problematic.
:iagree: This valve is 50 years old and may have the original rubber seal in it, also the current opening temp is unknown at this point. If it was my carb, I would block it off to not have any potential effect on the tune. :alan2cents:
Quote from: bennydodge on March 02, 2020, 11:27:47 AM
Quote from: 734406PK on March 02, 2020, 10:10:23 AM
Quote from: kawahonda on March 02, 2020, 09:44:48 AM
So I should inquire about boosters that have the larger jet installed since its kind of a one piece ordeal. I don't see a lot on eBay, and without a part # is it going to be anyone's guess as to what size the built-in jet is?
Question here: Are they all .031, or are certain carters .033?
Another question: Are the AFB boosters interchangeable with the AVS? Probably not.
I'd hate to drill out my originals here...would rather get another set that has the correct size, or to drill a "spare" set.
If they are all .031", then it's probably best to attack this last and only if needed. That's my thinking.
I'll definitely ask/obtain about the .098 jet.
I don't think I'll need to mess with the main jet for now since I have two needle sizes to try on the way!
Trying to find a pair .033" boosters is going to be tough without a part number IMO. The idle jet size,air bleed etc will be application specific but ask Uscarburetor, you never know...
The idle jets can be filled/crimped and drilled back out to.031" if needed but i doubt you will have to do that, you have plenty of adjustment in the idle mixture screws.
If you zoom in on the second photo that bennydodge posted, there is a Carter suggested carb tune for a modified 340, pretty interesting, staggered jetting. :bigthumb:
I noticed the staggered deal as well-and those guys really tested this stuff back then, sharp dudes for sure...
Carter Engineering must have done this on a dyno with a pyrometer on every cylinder, Very Cool! Great Info! :bigthumb:
I'm trying to study the Edelbrock tuning charts and I'm wondering if I'm thinking about it backwards.
There's the thick part of the metering rod, the middle part (slightly less thick and very hard to visually see), and the pointed end of the rod (thin).
What part of the 3-stage metering rod is responsible for what in Edelbrock's terms ("Power" and "Cruise")? I assume one part is partly responsible for idle, the center (transition/cruise) and the other for WOT?
It appears by the charts that the "thick" part of the rod is responsible for cruise, and the "thin" part of the road is responsible for power. Not sure where the center plays in.
Trying to figure out which metering rod that I ordered should I try out first. The "mildest" one has the same "thick" part as my current, but .002 thinner center and .002 thinner tip.
Quote from: kawahonda on March 02, 2020, 01:14:36 PM
I'm trying to study the Edelbrock tuning charts and I'm wondering if I'm thinking about it backwards.
There's the thick part of the metering rod, the middle part (slightly less thick and very hard to visually see), and the pointed end of the rod (thin).
What part of the 3-stage metering rod is responsible for what in Edelbrock's terms ("Power" and "Cruise")? I assume one part is partly responsible for idle, the center (transition/cruise) and the other for WOT?
It appears by the charts that the "thick" part of the rod is responsible for cruise, and the "thin" part of the road is responsible for power. Not sure where the center plays in.
Trying to figure out which metering rod that I ordered should I try out first. The "mildest" one has the same "thick" part as my current, but .002 thinner center and .002 thinner tip.
Edelbrock terms are for 2 step rods. "Power" is the thin end. "Cruise" is the thick part. 3 step rods used in the AVS have a mid section for greater metering control that's in between "cruise" and "power". More expensive to machine a 3 step rod. Try the smaller more aggressive rods first, then maybe trim it back to the mild and see if there is a difference. You might want to try different springs also.
Sounds good.
Air horn off.
Confirmed .096" in secondaries.
Confirmed booster is likely .031. .0325 bit won't fit it.
Here's some math, followed by a "guesstimate" chart.
Assumption: The "middle" position of the rod slightly impacts BOTH sides a hair (power and cruise). Could be a faulty assumption?
Assumption: Any change over .03" makes a "step" movement in the grid (excluding the middle). This seems to be true looking at Edelbrock's charts.
Assumption: "baseline" is lean likely across the board.
Stock Rod: .065 x .064 x .055
Rod 1 (en route): .065 x .062 x .053
Rod 2 (en route): .063 x .060 x .051
Rod 3 (hard to find): .0635 x .060 x .055
If the center of the 3 step road has no bearing on the Power and Cruise axes, then it would look like this:
Rod 2 still looks like the winner regardless!
That's ingenious! And here i was concerned about confusing the situation with too much math! :unbelievable: I agree rod 2 will have the most fuel enrichment. I hope its enough, now only if we had AFR readings...
IMO:
Assumption 1 Yes
Assumption 2 A stage (Step) is 4%
Assumption 3 Yes, Ethanol blended fuel of today is far from what it was for the original calibration.
Here is another chart that may be of use:
https://www.rasoenterprises.com/images/documents/carburetion/CarterAFB-MRJ.pdf
Thinking ahead as I'm now only waiting for the .098 secondaries before I can retry everything.
If I had to, instead of drilling, I was talking to Neil and one could simply reduce the air volume of the air bleed sizes on the top.
I however don't know which one as each booster as two .033" air bleed holes.
I do have .022" wire, which might be a little too thick, but I'm thinking that sticking an appropriate sized wire in the air airbleed should perform the same action as drilling.
The rear hole is the main jet & front is the idle bleed
Give it a try and see what happens. The mixture screws should need to be screwed in a bit to correct the idle mixture going rich.
Cool. I figured that will be my next step when/if the air horn needs to come off again. For now, I want to assess the metering rod change and the secondary jet change. I also changed my .046 (drilled) nozzle back to to the .043 nozzle. Since I have a good understanding of when transistions happen, that shouldn't get in the way of anything. And besides, going from the .043 to the .046 didn't really do anything anyways. Preferably, I'd like to dial that back even further, or maybe go to the "middle" position on the arm, but that's not what I'm focused on yet!
Do you guys think my .022 wire is a bit too thick, or still just worth trying anyways? That leaves .011" of air space in each bleed. How long does the wire need to be...stick it in all the way until it "bottoms", and then make an bend on the top like an "L"?
You want to bend the wire into an L shape and only plug the air bleed. You don't want the wire so long that it blocks the idle fuel jet. A .022" wire will enrich the idle circuit but i can't tell how much or to cross the effect to a drill size for the idle jet, its all an experiment. Lets see if it works first. I think it will.
it will definatly have an effect , thinner wire should work better , I would make it drop in 1/2 approx & hook the top end
Cool. I'll plan to get some .015" soldering wire and make it go in about 3/4" or so.
you should be able to pull a single strand out of 16 or 18 ga stranded wire
I just scored some from a friend! .015"
Just a "hook" at the end I suppose is all she needs. Have it go into the air bleed around an inch or so?
The good news is when I get to tuning this weekend, I'll have everything on-hand.
Yes just hook the end so it cannot fall in or out !
It will need more of a hook to keep it from coming "out" though. Maybe I'll just "wrap" the end around the booster. That will secure it.
sure
Fired it up.
Warming up now.
Rich right off the bat just from a metering rod change....
Letting it warm up. I don't think air bleed mod is necessary.
Alright. Got it nice and hot and performed these changes. I used the .063 x .060 x .051 rod. The .065 x .064 x .055 was replaced. I also upped my secondary jets to .098 over .096.
First off, it idled rich without any adjustments. With the mixture screws out 3 3/4 turns, this is to be expected. Good so far!
I achieved highest idle/best vacuum at 3 turns from out with new needles. I kept my timing at 13 initial, which is a bit low for my recurve.
Drove it 6 miles. Stopped and went. Stopped and went. I probably looked stupid, but for the life of me I could not get it to hesitate or stall anymore. I got on it a few times and did not experience any "rich" signs ("bog" or rich stumbles).
Success. It does not need the idle bleed mod.
Next steps:
1) Get timing back up to 15-17 degrees, right before detonation.
2) Start leaning accelerator pump. First try second position with .043. If bored/have too much time on hand, install factory .033 and try that out.
3) Get to spark plugs to monitor change over time.
Awesome job! Congrats! Readjust the idle speed and mixture screws after the timing change then check the plug color after some use, should be tan. :bigthumb:
Thanks. My dizzy guy said to not touch timing If speckles are present.
I still may go up a degree. I always need to understand limits before you can understand optimal.
Basically, time to hone in on the pumpshot next.
Quote:
Thanks. My dizzy guy said to not touch timing If speckles are present.
He is a wise man, old school i suspect! FYI, speckles WERE present bit since the mixture change, things are different now.
I still may go up a degree. I always need to understand limits before you can understand optimal.
I Agree!
Basically, time to hone in on the pumpshot next.
Sure, check the limits, this is how tuning goes. :bigthumb:
Idle mixture screws don't seem to need to much adjustment (if any) from a small timing change (it seems).
I raised it to 15 initial. I hear some very faint, intermittent pinging at full load. Took about 10 minutes to discover the pinging at this setting (with just me in the car).
So I lowered it to 14 initial. Will test that setting tomorrow.
Got some new Champion plugs. Once I determine a timing setting with NO pinging whatsoever, then I will change plugs.
Then it's time to play with that pump! I'll probably just move arm to the center hole and probably stop tuning from there. Not sure if the effort is worth it to install the .033" when everything seems fixed! Who knows...I like toying with stuff. Nozzle size: Timing. Arm position: Volume.
btw, STILL NO stumble anymore. :)
14 initial seems to be the ticket. No pinging, so I'll leave it there and monitor.
I moved the pump to the second position and reset the height.
Went for a drive and didn't notice any "negative" change. Maybe it was more "snappy", but that could just be a false perception. So I'll keep it there for the time being. I don't see a reason to go lower than the .043 nozzle at this point--that may just be playing with fire.
There is no doubt that I picked up power down low from this change. Peeling out, doing burnouts is much easier to do now.
From a stand-still, if I SMASH the gas pedal ALL the way, 40% of the time it would perform as expected, 60% of the time there would be a micro-hesitation. This could simply be an adjustment of the air-door? I didn't try this "smash foot down 100% from standstill test" at the richest pump lever position but I don't think that would impact this test in any way. The lever position just changes volume, not timing.
There really isn't a use case where one would smash the pedal from a stand still. Drag racing you would hold the brake and raise the RPM to stall level. Same process for doing burnouts, just more brake.
So I'm not sure if it's worth "tuning" this part out, lol. But yea, I haven't touched my air door yet as I didn't really have a reason to...there is no hesitation from cruise to WOT. So I wouldn't really know how to "test" my air-door change.
Is there a way that I can give it more idle speed during warm-up? She basically is warming up at about 500ish RPM, which is a bit too low.
Yes there is a fast idle cam , a rod from the choke plate runs down to it & there will be a screw that rides on the can to raise the cold idle rpm
Congrats on getting it mostly tuned up
Best method to play with that? I suppose wait until it's cold, remove air cleaner (for access), then fire it up, run over to engine bay, and start tightening that small screw on the driver's side that's underneath-ish?
Regarding the WOT from idle "micro" stumble (that i'm really not motivated to get perfect), I think that's best solved by an AFR gauge to save time/money. Again, I don't know of any use case that requires the driver to floor the pedal from a stand-still without any brake action. Would be interesting however though if the "wire" idle bleed mod could probably solve that. Keep in mind it doesn't do it every time. So IDK...?
It's amazing how much better this car drives now. Since I'm adding a 408 stroker motor soon with yet another AVS carb, I think it's best to call it quits here--but definitely raise the fast-idle speed. This is ready to hit the drag strip and can run consistent runs each time. Guessing 14.8 ET.
Keep in mind, the "testing" that I'm now talking about is not "drivability testing". I've since moved on to "reckless driving ticket" find-a-place-where-no-one-is-around testing where I have to be careful. :) Not a bad tuning job so far, eh?
Choke is on (I still have to do it by hand, the bi metallic coil doesn't give it enough upwards pressure to open the choke)....unless something else isn't right.
Set screw isn't near the steps on the cam...
Solved the divorced choke rod issue. Basically, it wasn't applying enough upward pressure to "overcome" the slight friction in order to flip the choke plate closed. This is likely because of the 5/16" (or whatever) carb gasket I am using for heat soak. A couple minutes with pliers allowed me to lengthen the rod in order for it to accurately 100% apply the right amount of pressure when cold.
Yay, no more having to pop open the hood to "flick" up the mechanism anymore.
Now, to figure out how this fast idle/cam linkage thing works.
Check the factory shop manual (FSM) for the best procedure explanation on AVS linkage adjustment. Fairly simple bending of link rods to a specific dimension. Congrats on solving your issue!
I ordered a step up spring kit for final tuning.
My understanding is to warm engine, place in gear, and read vacuum.
Divide by 2, and go with that spring?
I have not tested my vacuum in gear, but I'm 16" in park. Probably 14-15 in gear as a guess.
I assume the factory Carter ones are 8?
Quote from: kawahonda on March 11, 2020, 09:35:06 PM
I ordered a step up spring kit for final tuning.
My understanding is to warm engine, place in gear, and read vacuum.
Divide by 2, and go with that spring?
I have not tested my vacuum in gear, but I'm 16" in park. Probably 14-15 in gear as a guess.
I assume the factory Carter ones are 8?
Yes that's the Edelbrock recommended starting point for metering rod springs 1/2 idle vacuum in gear. Keep in mind that the lower the spring tension the later the metering rods come into play (lift off from cruise to power). OEM are probably 8-10 inHg springs when new. They are color coded today.
Cool. Sounds like firmer is better and I should prob leave it alone at my vacuum. At least I have them on hand!
I'll continue to look at the fast idle engage. I have a rebuilt AVS on the desk and it also does not engage the fast idle during bench testing.
Would be nice if someone could shoot some pictures of a know working one so I can see how all the linkages should work.
Quote from: kawahonda on March 11, 2020, 10:02:29 PM
Cool. Sounds like firmer is better and I should prob leave it alone at my vacuum. At least I have them on hand!
I'll continue to look at the fast idle engage. I have a rebuilt AVS on the desk and it also does not engage the fast idle during bench testing.
Would be nice if someone could shoot some pictures of a know working one so I can see how all the linkages should work.
This should do it http://www.moparts.org/Tech/Archive/fuel/14.html
Here's the problem with mine, and the one on my bench. Maybe I still don't understand how it works.
1) The bimetallic choke will apply upward pressure when engine is cold This will push the choke plate closed using the linkage on the passenger side of the vehicle. Solved by lengthening the rod to account for carb spacer.
2) This same linkage runs through the carb and "kicks" this flipper on the driver's side of the car. I marked the flipper. There is only ONE way to install this, because the flipper has a pre-drilled location for this linkage that runs through (aka, non-adjustable).
3) That flipper then "kicks" the surrounding linkage.....SUPPOSEDLY enough to kick the cam under the fast idle screw. This just ain't happening, or it's not anywhere close to opening. This surroudning linkage doesn't move at all, choke on or off.
Make sure the tab on the upper arm contacts the plate (flipper) and pushes it counter-clockwise, pulling the fast idle rod upwards...
If that is making good contact, and pulls rod upwards, then check to lower pivot plate to make sure that it isn't seized on the shaft...
You should be able to move everything by hand freely, and get fast idle screw to hit cam...
Yep, the tab contacts plate on the driver's side, but the allowable movement isn't enough to really rotate enough to cause a big movement of the fast idle cam area.
All pivots move freely. Nothing appears or seems seized.
To make sure I understand operation correctly.
It all starts with the choke, either from the choke well or from an electric choke. When cold, the linkage (from the choke unit) on the passenger side develops pressure and applies it to the passenger side choke linkage that will "push" the choke on (the choke plate closes). This linkage connects to the driver's side (via inside the carb) and pushes the flipper on another plate, which pulls the bottom linkage towards engaging the fast idle cam. HOWEVER, without any movement of gas pedal, I would EXPECT that the edge of the fast idle cam (not the "engaged face") will push against the fast idle cam screw (under some pressure). Once the throttle is activated (probably around 1/2 way is all that's needed for a few pumps), the fast idle screw gets "out of the way" and allows the cam to lock into the fast idle position. From here, you simply just fire up the car. As the engine warms up, the choke plate will slowly open, which in turn will rotate the fast idle cam to a lower RPM "notch" during warming. As soon as you "blip" the throttle with the choke is fully off, the cam should rotate out of the way.
Do I at least have the mental model down on correct operation?
If so, the cam is not pressing against the edge fast idle screw when the choke is activated.
What I really need to see is a series of actual pictures of an AVS with a working fast-idle linkage from start to finish, where/how all linkages are positioned, and maximum movement of each. Seeing pictures of AFBs, Edelbrock AVSs, etc doesn't really help since the minor differences/different linkage designs won't be fully applicable.
My dad is coming into town tomorrow and is excited to solve this. But I'd always strive to solve it before him, or at least, go into it with the correct mental model of operation with him.
What's interesting is BOTH of my AVS carbs perform this way, and are assumed to be assembled correctly. Not having fast idle cam operation is not a deal breaker or anything, but it's nice to have.
Maybe I can shoot a video of the AVS on the bench and post it here.
You are correct in your understanding of the way the carb should be working :bigthumb:
Nice to see you're getting a handle on the tune-amazing what a little extra fuel will do :cheers:. Make sure that you depress the throttle FULLY on a cold engine(sitting overnight). This will completely engage the fast idle cam.
better PDF https://quadrajetparts.com/pdfs/4052C.pdf
Figure 5 is the adjustment I think your needing ...
(https://forum.e-bodies.org/dlattach/;topic=14980.0;attach=133090;image)
Here's a similar unit for reference ... DO I see one major difference in the upper shaft items in the way they are assembled ?
(https://n.b5z.net/i/u/6149764/i/Figure2.jpg)
another put together the same way
http://www.2040-parts.com/-68-69-chrysler-dodge-plymouth-carburetor-4711sa-c-4-avs-340-383-413-4-bbl-i529815/
Oh hell!
That explains it.
Quote from: Bullitt- on March 12, 2020, 04:38:50 PM
better PDF https://quadrajetparts.com/pdfs/4052C.pdf
Figure 5 is the adjustment I think your needing ...
(https://forum.e-bodies.org/dlattach/;topic=14980.0;attach=133090;image)
Here's a similar unit for reference ... DO I see one major difference in the upper shaft items in the way they are assembled ?
(https://n.b5z.net/i/u/6149764/i/Figure2.jpg)
another put together the same way
http://www.2040-parts.com/-68-69-chrysler-dodge-plymouth-carburetor-4711sa-c-4-avs-340-383-413-4-bbl-i529815/
YUP, Good eye! :worship: :worship:
Alright, I located the tang" in the correct spot.
The fast idle cam now engages.
It appears I had a misunderstanding.
The choke well linkage shouldn't be so long as to "automatically" activate the choke when cold. I basically was adjusting (lengthening) this linkage without the fast idle "mode" engaged. This creates a 100% fully closed choke scenario that will cause an engine to never start. :)
Basically, it appears that "correct" operation does NOT start with the bimetallic choke linkage. It begins when the A) engine is cold, and b) gas pedal being pushed to the floor and back. THIS action activates the fast idle cam, and this activates the "setting" of the choke plate/valve and is THEN when the bimetallic choke well linkage/tension comes into play....
I set my fast idle to 1000 RPM. It appears that the book wants me to do 2000 RPM. Seems a lot to me. Is the idea that 2000 RPM warms the engine faster?
i believe the 2000 rpm spec is set with a warm engine, this will give you about 1500 rpm cold. You can adjust your cold idle to whatever is comfortable.
I feel like it's in bad taste to leave a thread without conclusion for future readers.
1) The metering rod change solved off-idle stumble completely, regardless of engine temp. I agree with many people are falsely writing this as an "accelerator pump" issue. If you can capture this stumble by "slowly" (but progressively) pushing on the throttle, it's NOT a pump issue.
2) The rod change seemed to allow me to advance 1 extra degree without any signs of pinging with 91 blended fuel. I am now at 14 degrees initial, from 13 degrees. I will keep testing this and maybe when it's 100F outside I may go down to 13, but it appears that extra fuel in the middle and WOT stage helps predetonation by a marginal amount. When it's 65F outside, I CANNOT get it to ping with anything I do, fully "hot", even with a passenger in the car. Before the metering rod change, it would!
Regarding the fast-idle cam function, DO NOT adjust the well choke well linkage unless the fast idle cam is engaged. You surprisingly will not read about this in any of the "master" books. The choke well linkage should be set ("bent") ONLY when the fast idle cam is engaged. The manual/rebuild guides state the choke plate clearance, and that's what you should use. Too big: Won't start. Too small: won't start. It has to be very close to what it says, with fast idle cam engaged! It's GENERALLY around 1.75mm.
I have tested my settings twice now. Pump pedal to the floor ONCE, then fire up. It will fire up, and run at 700, then to 1000 RPM, then slowly it will get up to whatever the fast idle is set to (in my case, 1200 RPM). At that time (a minute or so) once you touch the throttle, it probably will revert back to your normal idle speed (in my case, 850 RPM).
Yay.
THE RPM that you should set this to is just enough to keep the engine running to successfully during warm up (leave pedal alone). This could be anywhere from 1,000-1,500 depending on your location/alt/temp. The book states "2,000 RPM", but that's a REALLY rough guideline. you should set the RPM to where the engine can keep running without your help as it warms up. For me, that's 1200 RPM.
I JUST changed the plugs, but here is the SAME plug before and after jet change.
Let me know what you guys think. I bet there's still some more tuning to be had.
I'll take a picture of the new plug after I get some miles on it.
looks pretty good or a bit rich with the black on the cermaic
BTW rich is cooler / safer side to be on
Apparently, 8 miles isn't enough for a new plug reading? LOL
8 Miles isn't enough time to tell, but the plugs do look to be running cooler IMO. Put 50-100 average driving miles on them and recheck all of the plugs. :bigthumb:
now it still looks lean which makes more sense as you had to richen it to eliminate the stumble , could go a bit richer yet
Yea, I'll drive it some more and recheck the plug. Sadly, I'm basically at Carter's smallest most-available 3-step rod. The next size down would be the 16-216 (.0625 x .058 x .047) which was probably some engine-specific rod set and I'm not a fan of how much it would richen out WOT. Not really anything left after that if I were to stay with the 3-step metering rod, unless I bump up my primary high step jet from .089 to .098, then see what's available for the "fat" rods. Not sure what implications that has?
Right now it has #16-404 (.063 x .060 x .051). What the ECS 340 carb came with was .065 x .064 x .055. I'd hope that the plug will tell me which portion is lean/rich so I can fine tune more. It feels like I'm close. I wouldn't be surprised after a few more miles if that plug turns out to look pretty good! What parts are looking lean so far?
I could do the flat-top two-step rod conversion on it (I have all the parts necessary).
At least you know what's going through my head right now. I definitely improved the tuning dramatically. I've driven it about 20 miles since the rod change. It will micro-stumble if I abuse it from a stand-still (like smashing the pedal) slightly over half of the time, but hard to say if that's a jetting issue or if I should plug those idle bleeds some. I wonder if AVS carbs will never work "perfectly" unless the idle mix screws are out past certain amount of turns? I went from 3 3/4 turns from "out" to 3 turns from out after that rod change.
I can still get it to stumble (slight, nothing like before) by doing some really quick (aggressive) pedal presses (20% down), but it's really few and far in-between now. Driving it with normal foot work there are no stumbles like before. I know I said "solved it completely" above, but it really took a lot more driving to still find some very sporadic causes of it still being there depending on the vehicles load from standstill and the aggressiveness of my foot trying to "make" it do it, but its very inconsistent now and doesn't happen often. Maybe I enjoy spinning the tires much easier now....:)
Best to wait to see how the plugs look. This is definitely getting into the "fine tune" phase.
And with the 408 + 440 AVS carb build, I get to restart this process again. So It pays for me to get it perfect. :)
I wouldn't jump that big of a jet, you'd be right back to square one. You can polish the rods with emery cloth to take a thou off one or all stages but I wouldn't screw around with it unless you have a spare set.
Some more information. I think I'm on to something here.
I put in my program a "what if" I could find a .098 tall orafice given what's available on eBay, and can I possibly find a rod that would give me a stage richer or so. The answer is no, the largest available rod on eBay is a 15-564 which is .068 x .065 x .062. The percentage change richer would be too much.
I did however find a rod that may be worth ordering to have on hand that would pair well with the factory .089 jet. It is listed as "Option 1" below (16-565). I'm thinking that may be worth ordering right now to have on hand just in case. It would only require "emery-clothing" just the tips to richen the WOT where it's needed, but the "cruise" and "transition" area look great.
I'm wondering about what exactly the hell that middle stage is for. It seems to be to be mainly for fuel economy or fuel emissions. I'm wondering that off-idle stumbles from agressive foot behaivor can be related to:
1) Accelerator pump nozzle. However, I am using the largest avail nozzle @ .043. Going more just seems to be compensating for something else.
2) The idle mix, even though set properly, has the air mixture screws 3-turns from in (it was 3.5-3.75 turns with original rods). I wonder if 2, or 2.5 turns from in from a starting point impacts off idle-performance. Solving this would require:
a) Richening out the "cruise" portion of the rod. However, this seems improper. The plug reading is what should determine any jet/rod change, so that's why I'm saying we wait to read this plug.
b) Restricting the air space in the idle bleed (or drilling out oriface). This would allow screws to be turned inwards more (less air needed). However, my Carter 440 AVS also has .030 air bleeds, same as 340 carbs. I'd be curious what the modern
edelbrock AVS carbs have for an idle orriface.
3) The "transition" portion of the metering rod being too lean.
This is what drives me crazy ...
Why alter all 3 to change one ?
The middle position is transition . 12% change seems far too big for 1 step , if you have 2 of the same rods I would file the fat part down a bit
The % change is compared to stock rod only.
It would help for me to have a vacuum gauge in the car, but I'm assuming the middle step in the 3-step rod primarily comes into play in-between Cruise -> WOT, purely the transition there? From off-idle to cruise, even with an aggressive 40% gas pedal push (not flooring it), that is still the "fat" part of the rod only?
If that's the case, the center part of the rod should be left alone, WOT should be left alone, and just the "fat" part of the rod should be shaved--that is if the spark plug reading warrants a change.
I'm curious if the Edelbrock AVS/AVS2 carbs have a larger booster nozzle than the Carter AVS ones do. It seems like a lot of the things that were designed on the Carter AVS were there for emissions--having a middle stepped rod and having a little .031" booster nozzle. Running modern, less efficienct fuel from them also doesn't help. Having a California ECS carb probably didn't help either. I'll get it perfect! Just planning ahead for what I'd do once I finally get a chance to get a good solid reading on the plugs.
I agree the fat part would be where I would focus
One thing that's going through my mind, correct my thinking.
Let's say the plug is perfect. I mean, as perfect as anyone would want to mess with without AFR gauge and such. At that point, if the intermittent stumble through aggressive driving is still present, wouldn't it make sense to then turn to the idle bleed mod? Let's say I stick a little wire in there. That will requiring tightening the mixture screws to reduce air. Obtain the highest vacuum. All good. Stumble fixed....but plug readings should remain the same, correct?
Basically, I'm asking if plugging the idle bleeds (or drilling it out, take your pick) then resetting mixture screws will lead to the same plug reading...
In my mind, it makes sense to get a good reading on the plug first, then determine next step. It may be that the plug reads pretty darn good. That tells me to not fuss with the metering rods anymore? If plug reading still shows a lean idle, then that quickly means to focus on the fat part of the rod.
I think so yes. In my experience you will get it pretty good without an AFR gauge too, it just takes longer. After setting my 528 up and figuring I had it, I finally bought an AFR gauge to get it closer. I was a bit surprised that I had it right on using ears, nose and sparkplugs. Just be happy you have a single carb and no staggered jetting.
sure try restricting the bleeds , nothing to lose but time
After 30 miles. Still needs more time I think.
I can color a plug in a 1/4 mile
30 miles and that clean , I believe it could be richer
Richer across the board?
If so, that makes me feel very good about the set that I just ordered......just need to emery the tips.
This really is evidence that the 340 could do with the 440 AVS carb if so.
I have no clue how you are driving it , if you are idling a lot then just the idle screws need adjustment , if you are cruising then the thickest part of the rod is too large , , I usually find a wide open area or drag strip & do an extended WOT , shut the car off coast to a stop & see what color the plugs are to test WOT / rods up smallest part of the rods
Yep, I have never done an official WOT plug chop. Too many damn cars on the roads today and not a lot of pull-off spots.
Very little idle time with what you see. Idle is set to highest vacuum reading. What you see is mostly cruising/city and slightly aggressive off-idles during take-offs. I WOT'd as much as I could, within reason. I left a bit ass F%*$ing patch in parking lot before coming home. Fiance said she will never rid with me again.
Does that help anything or not really? What's a safe way to turn off the car....shift to neutral first, then turn key off?
The new rods that are coming rich out the cruise by a step, but it also riches out transition. It's an interesting rod.
If you don't like that idea, I have another set of rods that would be pretty fair game for emery-cloth....
Current: .063 x .060 x .051
Stock: .065 x .064 x .055
In mail: .0615 x .058 x .055
Rods that may be interesting to modify: .065 x .062 x .053
Come on Neil, 3 step rods make it fun....and Carters look sexy.
What you are seeing then is rods down , so if you have different rods that will richen it a step I would do that first
FYI be very careful shutting down from WOT , do Not lock the steering just go back 1 click & yes I would go to Neutral .
WOT Is rods up .
Sounds like you'd plug the "in mail" rods in right away!
:yes:
Installed .0615 x .058 x .055 rod. Worked the .055 to .050.
Drove it 10 miles.
No stumbles at all.
I'm a bit floored why/how I picked up low end horsepower/torque. Spinning tires is easy with no lag or hesitation. Car is VERY responsive now.
My vacuum in park is 16 inches. My vacuum in drive is 13.5 inches. I have the stock step-up springs, but also have the assortment pack. Should I leave them be?
Did your fiance go with you ?
it still needs more fuel but it is better , more color
Going to leave her right there for now.
Does the insulator take more time to get color? That's WOT, correct?
No if it was going to color it would have color now , it may color differently cruising vs WOT requiring a change
What's your thoughts on step up springs? Going softer is basically going leaner. Pink spring is rated at 7" vacuum (14") and is closest to my vacuum in drive.
I would leave them.
:iagree:
Going to have my dizzy guy take another look at my distributor. I'm starting to question 14 initial. Usual "around city", "peeling out" stuff is fine, but get that engine really spinning on the highway and floor it (best way to add "load)...I'm STARTING to think I hear some very faint pinging. It's intermittent and has me questioning my self, which is already a decent sign to back off 1 degree: tells me I should reduce it to 13. Kinda weird running a recurved distributor at 13 initial. I'm going to ask my guy if it makes sense for him to reduce mechanical down. No reason this car shouldn't be playing at 15-16 initial, and for it to be completely safe at that.
For your enjoyment, here's some videos I took today after rod change.
"aggressive" foot during dead stop:
Doing a little burnout....It used to take a lot of effort (having to load engine a lot, and hope for no stumbles). Now it was just a quick and easy thing:
These videos may seem weak, but It was running so lean where doing any of that consistently was a chore and by chance. Ignore my stupid voice of excitement, but I was very shocked at the difference these rods made compared to the last rods (which made a positive difference too).
I was watching an episode on Tony's Garage, and he mentioned something interesting. If some cylinders are burning leaner/richer, then it's common to change jets that are corresponding to those said cylinders. I was thinking about that! May be good to keep that in mind and mark/document plugs after another 50 miles.
1 3
1 3
2 4
2 4
front
1 = passenger side, secondary
2 = passenger side, primary
3 = driver's side, secondary
4 = driver's side, primary
If one whole side is showing leaner cruise readings, I'd assume that probably means a metering rod change only if a cruise reading.
In practice, it's probably much harder than it sounds though and requires you to isolate cruise vs WOT for readings. Interesting though, and explains why the awesome literature that was posted a few pages back shows a tuned 340 having offset jetting/rods.
On a dual plane intake the jet listed would not affect the cyl in you diagram ,
so you would have #1 4 on the same jet
INTERESTING. See, that's good for me to know.
1 and 4 = same jet (that means both primary/secondary systems)
2 and 3 = same jet
That would make plug readings much more interesting....
Follow the path of the intake you shoudl be able to see which runners are connected together
Is it true that WOT jetting (secondaries) can only be checked by the "turn-off" method and cutting the plug to look at base of insulator?
Basically yes , idling down can add or remove color , however we know you are lean so you have felt the difference in changing the primary side with different rods so you should be able to feel if it is improving by richening the secondary side also & use the plug color for backup
Maybe as I wait for my distributor to get back from Hillside for a diagnostic/check-up, I'll throw these 100's in.
Carb started with .096 (ECS spec)
changed to .098 awhile ago. Prob still lean.
.100 prob isn't a bad idea.
I'm looking to REALLY nail in the pump shot.
I noticed today that I have some slight throttle movement before I see fuel come out. It's pretty slight, and I've only tried with a slow motion of moving the throttle.
If I wanted the pump shot to happen a fraction of a second quicker, is that raising, or lowering the stem? I'm assuming the best possible setup is if you simply just put ANY motion whatsoever, even slight, you should see fuel come out of the squirters.
I remeasured my stem at it's 11.5mm. Factory measurement I think is 11.2.
You may get desired result by adjusting/shortening the linkage to the accelerator pump
The hole closer to the carb body I believe delivers a quicker complete shot as it doesn't have to move as much for full travel