Carter AVS Lean Spot

[kawahonda]

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?

[734406PK]

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.

[kawahonda]

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.

[kawahonda]

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.

[Chryco Psycho]

looks pretty good or a bit rich with the black on the cermaic

[Chryco Psycho]

BTW rich is cooler / safer side to be on

[kawahonda]

Apparently, 8 miles isn't enough for a new plug reading? LOL

[734406PK]

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. 

[Chryco Psycho]

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

[kawahonda]

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.

[RUNCHARGER]

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.

[kawahonda]

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.

[Chryco Psycho]

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

[kawahonda]

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.

[Chryco Psycho]

I agree the fat part would be where I would focus