Carter AVS Lean Spot

[bennydodge]

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.

I noticed the staggered deal as well-and those guys really tested this stuff back then, sharp dudes for sure...

[734406PK]

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.

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. 

[734406PK]

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.

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!

[kawahonda]

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.

[734406PK]

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.

[kawahonda]

Sounds good.

Air horn off.

Confirmed .096" in secondaries.

Confirmed booster is likely .031. .0325 bit won't fit it.

[kawahonda]

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

[kawahonda]

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!

[734406PK]

 That's ingenious! And here i was concerned about confusing the situation with too much math! 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

[kawahonda]

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.

[Chryco Psycho]

The rear hole is the main jet & front is the idle bleed

[734406PK]

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. 

[kawahonda]

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"?

[734406PK]

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.

[Chryco Psycho]

it will definatly have an effect , thinner wire should work better , I would make it drop in 1/2 approx & hook the top end