Carter AVS Lean Spot

[kawahonda]

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.

[kawahonda]

I would drill the squirter 

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.

[bennydodge]

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.

[bennydodge]

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

[bennydodge]

Long shot here, excessive slack in the throttle cable. I suppose lots of slack could create the "sensation" of a hesitation.

[kawahonda]

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.

[Chryco Psycho]

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

[bennydodge]

Progress indeed. Sounds like the secondary air door needs tightening now.

[Chryco Psycho]

or 1 step richer in cruise jetting

[kawahonda]

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!

[734406PK]

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.

[kawahonda]

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.

[bennydodge]

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.

[734406PK]

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.

[bennydodge]

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.