Carter AVS vs Holley 3310 vs Thermoquad -carb issues -UPDATE

Been having some problems with the 4640SA Carter AVS on my 69 Charger. Its a very mild 440; six pack flat tops that sit .005" below the deck, 452 heads, K6401 Summit cam, stock 70 AVS intake manifold, TTI headers into 2.5" duals and an h-pipe, 3.23 sure grip. Since I put the carb on almost a year ago. It has been completely rebuilt, all passages blown out with 140psi of compressed air, HIC blocked off, new floats, etc. My problem with it is it doesnt seem to idle right. The mixture screws are almost 4 turns out, to the point I had to stretch out the springs on the screws to keep them tight. Any further in and it starts idling like garbage. It will literally burn your eyes standing behind it. I switched over to the two step Edelbrock rods and jets on the primary side. Im currently running 70/47 rods, and .113 jets...secondaries are .098s. After a drive, the plugs are a very dark brown. I need to lean out the cruise side and was going to try out some 73/47 rods. Distributor is at 14 initial, 35 total, all in by 2200rpm. I picked up a fresh Holley 3310 (750) from a friend of mine, and I have a perfect 6322s Thermoquad. Ive never been much of a Holley fan on the street, and always preferred Thermoquads. Im not a fan of squarebore/spreadbore adapter plates though.

I have been fighting this AVS for a while now, and am not a fan of spending $15 for a pair of rods, and over $10 for a pair of jets. A reason I have never been much of a Carter/Edelbrock fan. I have a complete Mopar Performance Holley jet kit with sizes ranging from 64 to 99. The Holley is tempting me, but dont like the idea of relocating the coil to put it on.

For a car like this that is cruised around on the weekends, run hard through the gears every time its driven, etc, which of the three carbs would be the best bet? The current AVS, the Holley, or the Thermoquad?

open up the idle jets .037" and the 4640 should purr.

That's another thing I was wondering about. I've never modified the internals of an AFB or AVS before. Which passages are the idle jets?

Holley

Not if the TQ is set up right !!

Awesome! So the tip of the idle fuel jet needs to be opened up a little bit? Do you recommend a good starting point?

the idle jet smog specs are .031" for an automatic trans. the 4spd cars were .035". i use .037" in my 4618s and it really smooths out the idle. most pre smog big block afb's were .035".

I'll have to give it a shot. .035" seems pretty big. I'll have to pull it apart, but it doesn't seem like the overall tube diameter is even .035"

first I would blast the clusters and the ports the idle mix screws are in with brake kleen. even tho it is rebuilt, something is way wrong with the carb (& that is a mild cam so not seeing how poor idle vacuum could be involved in this). lets get the carb squared away then fine tune the idle bleeds etc. do you have a "square" or close to it for the transfer slot?

That's what I figured. I've had the carb apart twice already, cleaned all of the passages out, blasted them with 130psi of compressed air. It's pulling 14 in/hg at idle. It pulls great for being such a mild motor in a heavy boat. It'll go sideways at 50mph when you open it up, I just need to get the idle situated

I'm assuming that the clusters ain't dripping from too much psi (& wouldn't think bad needle/seat cuz it has been kitted & likely a new filter, that it is definitely an idle circuit prob. some cluster gasket are cut poorly. did this carb idle OK any time prior to this. check the transfer slot when you can. what is the idle speed? EDIT you pretty much duplicated the OE jet/rod orifices?, maybe a bit richer which is good as all OE AVS's are lean & AVS strip kits are pretty much non existant tho I dont think the main metering would be into this if the transfer slot is pretty much a square

It has never idled right since I got the carb. I still have the factory rods and jets for it, I just changed over to the newer two step setup for tuneability. With the factory jetting, it was ridiculously lean at cruise, to the point it would miss and buck. I'm really not set on keeping this carb for any originality reasons. Nothing on this car is original. If I do start modding this carb though, there isn't any going back. That's why I was originally wondering about the Holley or the Thermoquad. I've had the TQ running like EFI on many engines in the past, and the Holley has been freshly gone through. Id almost rather pull the AVS and stick it aside if I'm going to have to start drilling passages open and modifying it

You are running the flat metering rod covers , correct , when you converted over to edelbrock parts , or did you epoxy the factory ones flat and smooth

Anyways

At idle with engine running , did you remove the metering rod covers and see if the metering rod pistons and rods where all the way down on both sides

it'll work. the tube small end is over .060" in o.d.

I run that same carb on my 71 BEE - 383 Magnum - Put the smaller AVS 6125 s up in the attic

Perfect - Carb is Awesome

I also blocked off the HIC

Made my own flat metering rod covers - Edelbrock doesn't sell them when I asked

104 Primaries
107 Secondaries

68-47 Metering Rods
Blue Edelbrock Metering Rod Springs , had to replace factory springs

Ill have to pull it apart again. Im using the flat metering rod covers from a spare Edelbrock I had laying around. The rods are down at idle and Im using 6 in/hg springs. Ill see about opening up those tubes. If that doesnt make any kind of a difference, Ill just have to try the 3310 or something

You're running 107s in the secondaries with a 383? Damn I'm only running 98s with my 440. I may have to dive into the secondary side once I get it idling right!

I would highly suggest not opening anything up (drilling). we gotta find/fix the root cause first.

The 4640 is for AC cars and I would look at the hot idle compensator for leaks (cork gasket) or block it like bee 71 said. Is your car AC? If not look for 4618 carb, they have different air adjusters. Check the rods to see if they are free moving and down when running, might not be seeing vacuum to pull down (restriction)

Like I said, the HIC is blocked off. The metering rods move freely, and are down at idle.

do you have any experience with changing idle feed/jets in any carbs?

The holly must be duel feed? Square bowl will fit with stock coil bracket, and I wouldn't put the tq on with an adapter. So find a 440 tq intake, less hassle since all the linkage and choke hooks up factory.

The root cause is the design. These are emissions carbs intended to run lean and they do; drivability problems were well known when the cars were brand new and today's gas exacerbates the original problem.

yes it is an emissions era carb & is lean & tweaking the innards does work excellent to fine tune em spot on but it can & will run at least on the idling circuit fine for the most part without em (& OP has a mild cam). there is another problem going on that needs to be fixed (something is severley damaged/leaking etc). I cant see fine tuning the innards with drilling fixing what is damaged. Like the one guy posted & my exp with em, they are fine but can be made better. if drilling mods fix this carb I'll be the first to admit I was wrong!

I'm with Lew and John on this one...... Drill 'em out.

Emission carb, in 1969?

You bet. All factory AVS's (Mopar started using them in '68) are emission carbs.

AGREED! Finding a good TQ is one thing. Getting parts to tune it is the other trick. Once you have a good TQ carb tuned in, there really quite an excellent carb. IMO, perfect for a street strip application.

A Holley is the easy way out. And I wouldn't blame a sole for going to one.

The TQ a least has the right Chrysler linkage, not a bandaid adapter.

B5XP29, FOR SURE holler how the AVS turns out! what you did to it/how it acts now. Inquiring minds want to know.

I ordered some #63 drill bits (.037"), as nobody local carries them. Hopefully they'll be here by the weekend. If I can't get the AVS running right, maybe I'll try the thermoquad. Thanks to everybody for the advice/suggestions

One of my favorite cars. Rode around many a nite in my friends 69 RT, forest green, he bought the car right off the showroom, paid for it himself.

The best bet is a brand new Holley 750 Street Demon, $346 delivered to your door. It looks a lot like a Thermoquad and has the latest metering ideas.

R.

Not interested in something the "looks like" a Thermoquad.

Question is, does it SOUND like one?

I like the Edelbrock 800avs in an application like this.

Well, it worked! Drilling out the idle fuel jet tube to .037" did the trick. It has never idled better. Smooth as silk. Who would have thought something so simple could have done it. Thanks to everyone that offered up the great advice! Gotta love Moparts! 👍

I also agree with you guys. Does anyone know what size the economizer or the other idle feed restriction is ? I take it that it is larger then the lower idle feed restriction at the bottom of the idle tube since drilling the idle restriction at the bottom of the tube helps and makes it richer ? Ron

Interesting , Awesome To Hear

By drilling them out , could you actually have cleaned them out , as in dirty or plugged ???

My 4640sa starts and idles perfect stone cold , idles cold with no choke not even touching the gas pedal , running the Mopar 284 / 484 Cam , transition off idle beyond smooth , I don't even want to try this , if not broke don't fix it ,since the many times I opened it up playing with jetting and fine tuning it

Anyways makes the Edelbrock 1407 that it replaced , man what a Headache that 1407 was , biggest POS carb I ever worked on

Not a chance. This carb couldnt have been any cleaner. I always clean all passages out with torch tip cleaners, carb cleaner, and a blast of over 120psi of air. Not every carb needs to be modified internally, but I guess this one did. Like I said, it has never idled better or cleaner, I leaned out the primary cruise step and fattened up the secondary jets while it was apart. Plugs look good, pulls harder, and idles great.

Awesome.... Good info rite here...