Avs 6125s on a 440

[pmschmitt]

So I have had my 69 300 for 3 years and it has always been pretty sluggish off the line and stumbled during quick acceleration, but run great during cruising highway. I have adjusted timing and mixture screws recently. When I adjusted the mixture screws it seemed I had to back them out almost all the way to keep the motor running in its happy place. The car was much more responsive underauick acceleration but still had a mild stumble. My next plan was to rebuild the AVS carb.

So I went about researching the correct carb rebuild kit only to find I currently am running an AVS 6125S on my 440 which is a 383 carb. Apparently the previous owner swapped this around. So here is my question do I get an AVS 4640S carb ( correct carb for 440 at/ac) for the car or do I purchase an aftermarket carb? I do not care about period correct etc I just want more performance and reliability. This car is a cruiser.

Also could this incorrect carb be causing the stumble in hard acceleration or is that just a worn out accelerator pump.

If aftermarket what is recommended?
750cfm?
Edelbrock?
Holley?
Demon?

Yes I know everyone has their particular preferences with carbs but just wanted to know what some of you were using that you liked.

 

[Turboomni]

I run an Edelbrock 1406 600 cfm on my 440. I never go over 6000 rpms and rely on the gobs of torque. Mine is a cruiser also

 

[66Newyorker]

I run a 625 cfm Street Demon. Had to richen it up for a 440, replaced jets and metering rods. Very good throttle response. Good at cruise.

 

[The Horvaths]

Holley Street Avenger.

 

[Wollfen]

Have a look at this, it is an all new design using modern technology and using the best parts of older carbs. Worth considering.

street demon 1904 750 Demon Carburetion Carburetor polymer bowl new in box look

 

[superfragl]

I run Edelbrock Performer 750. Very happy with it.

 

[70bigblockdodge]

Question about street demon for those of you that have one. Do they have small and large throttle bores? Like a TQ.

 

[The Horvaths]

One thing about the Street Demon; apparently they have very poor quality control. I've heard of many people being very unhappy with them. So buyer beware.

 

[pmschmitt]

Yes some other mopar forums said the same about the demon

 

[70bigblockdodge]

Never mind I finally found a picture of the bottom.

 

[pmschmitt]

I know a local guy selling a used Holley 750 3310-2 cheap, don't know much about hollers but I hear they can be very finicky

 

[The Horvaths]

I know a local guy selling a used Holley 750 3310-2 cheap, don't know much about hollers but I hear they can be very finicky

The old ones leaked and warped. You will have to rebuild the one you're looking at, (if it's not warped). The newer Holley's have fixed that problem. There is an awesome one for sale on this forum for $300. If you can't find it, I will link it.

 

[shooter65]

The 4640 is a 750cfm carb, don't know about the 6125. I can tell you that the 6125S is a factory installed carb. Dealer replacements were SA. ie. 6125S (Factory) 6125SA, replacement. That goes for all AVS carbs. If you want to stick with Carter and aren't worried about correct, you'll find an SA a lot cheaper than an S. If you sell your 6125S, it should bring extra money because it's not an SA. If you pick something else, you should get a 750cfm carb.

 

[pmschmitt]

Thanks

 

[BIGBARNEYCARS]

Do one thing for us with your AVS before swappin' anything. Pull the accelerator pump and remove the spring from the pump, lay it down and measure it. what ever the measurement iz take the spring by both endz and tenderly stretch the spring out by pulling it with both handz back and forth at the same time until you've added about 3/8", AND DON'T GO OVER 1/2". Reinstall the spring and the pump and see if your stumble iz still there.(Old guy trick with the AVS'z and 440z. BTW, If the pump iz not flexable and you can't get it to soften up(by soakin' it in ah little ATF over nite) replace it, Jer

 

[Wildaugust]

Kind of ironic in a way, LOL. The AVS that I'm using on my 383 is actually from a 440. It is a 625 cfm carb, however. After much searching, the only real difference between it and the 383 version, that I was able to find anyway, seems to be the size of the secondary jets. Both carbs are 625 cfm. The 383 version uses an .089 jet while the 440 version uses a .095 jet. I would assume the metering rods would be different too, but haven't found any reference to them.

Lots more info on AFBs it seems, not much on AVS. Strange.

There was a 750 cfm AVS, but I'm not referring to them.

 

[pmschmitt]

So went ahead and rebuilt the carb b/c I like a project and figured I'd see if it fixed the problem. Figured out the 6125S is a 630cfm carb with 0.089 metering jet primaries and 0.089 secondaries. I boogered up a primary that was stuck and ordered 2 new primaries from mikes carburetor.

The new primaries have a #389 on them and the old primaries have a #489 on them. They are also shorter than the original jets.

My secondary jets match the ones sent by mikes and are the same height and have the #389 stamped on them. Soooo... The question is can I use the new #389 jets for the primaries even though they appear too short?

Pics for reference

 

[commando1]

I say if the diameter of the hole is the same, it makes no difference but surer than hell some braniac is posting right now that the depth of the hole will cause atomization problems inversely proportional to the outlet side chamfer thus resulting is fuel dispersal patterns to be disrupted requiring....

 

[Polara_500]

The only thing I'd worry about would be if the metering rod is long enough to reach the 'neck' in the new jets? I can't tell if the height relative to the floor of the bowl is the same or if the old jet is effectively taller.

 

[Big_John]

The depth of the hole will cause atomization problems inversely proportional to the outlet side chamfer thus resulting is fuel dispersal patterns to be disrupted requiring....

But seriously.... It's been a while since I've had an AVS apart. I think there may be a problem. First, the metering rod and the jet have to match each other. If there is a height difference, the rod may be too far out and cause an over rich condition. Second, I think that jet seats on the top flange. It may not tighten correctly.

This is really a question for the guys that sent you that jet. I'm going from a faded memory and an idea of how it all works. I wouldn't use it until someone smarter than I am about it confirmed it was OK.