Carter AVS Lean Spot

[kawahonda]

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.

[headejm]

 

[Chryco Psycho]

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 

[kawahonda]

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?

[kawahonda]

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?

[734406PK]

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. 

[Chryco Psycho]

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 .

[Bullitt-]

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

[bennydodge]

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.

[bennydodge]

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..

[bennydodge]

One other thing-make sure the "s" link on top of the plunger stem is not installed backwards. Easy mistake to make...

[bennydodge]

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.

[kawahonda]

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.

[kawahonda]

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...

[bennydodge]

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