Strange Behavior Of New AVS2

[Speedbird]

Lots of chatter on here from people about this "new" model from Edelbrock.
Here's mine.
Old Carter AFB replacement
Edelbrock fitting
What's going on:
Broke the motor in with one of my Q jets. No problem. Wanted to use a "known good" carb. (See picture at above link)
Then I figured I'd buy my first ever new carb.
800 CFM. Why not?
I might put it on a bigger engine later. I just want to get down the road.
New engine deserves new carb.
383 mild cam. 3/8 line to stock fuel pump and 5/16 line to carb.
Now, set the idle speed and crack the throttle. Engine will not return to idle speed when throttle goes back to idle. Stays high.
No linkage binding. I'm doing if from the linkage watching the plates. Not on fast idle cam. Looked down carb don't see gas peeing.
Adjust idle screw to slow it down and the engine slows down and dies.
(The plates are closing more then when I set it down than when I initially set the idle speed.)
HUH?
Did I buy too big a carb? Can't be a fuel line delivery flow problem?
I've played with the idle mixture and doesn't help the problem.

Here it is today. I'll make it pretty later...if it ever works right.

 

[AR67GTX]

It’s probably bigger than you need but with the adjustable AVS secondary valve it should work. But those have pretty big bores, might be bigger than the openings in your intake - did you measure them and check? Could be the primaries are sticking and hanging in the intake bores.

Also, I’m not sure I know how you have the accelerator cable hooked up to it at present?

 

[Speedbird]

It's on an Edlebrock Performer 383 intake.
(I've got others. Even stock ones.) That's one reason I bought the carburetor.
Matched?
Cable is irrelevant. It's got slop. I'm thumbing it over the fender. Something is very weird.
It's just the idle staying fast after cracking the plates till I change the screw to slow it back down and then it dies.
(Closes the primary plates more.)
Do note the picture in my links above of the actual carb.
What everyone is showing on the net is a spread bore carb.
Which is what I really wanted. But I knew the pictures were wrong going in.

Oh, and people with a manual trans will still need that automatic adaptor.
I saw that and order it at the same time.

 

[Macdon221]

I read your initial post. You did say the linkages were not binding.

I just went through this. I looked at everything. Even thinking the weights in the Dist were hanging up changing the timing after a higher RPM....giving different timing at idle. The culprit were the secondarys. After opening the throttle (full open to set choke or hard acceleration) they were sticking open just ever so slightly....giving the faster idle when the primaries were fully closed. It was very hard to spot. Touching the linkage with my finger after the car was shut down the secondarys just "nudged" close. They were staying open like a 32nd! Not saying this is the issue...but thought I would pass it along. Something simple I have had in the past was also the CARB gasket was just a hair too small for the carb bores and the throttle plates were sticking open.

 

[gtxrt]

the size of the carb is not your idle problem. I would take the throttle cable off and try it. if not then take the carb off and make sure the gasket is not hanging over the bores. when putting the carb back on don't tighten the nuts all the way and open and close the throttle making sure no binding then tighten the nuts with the throttle wide open. if it still does it the dist advance might be kicking in.

 

[gtxrt]

looks like you moved the accelerator pump to the top hole Sometimes you have to bend the arm a little so it is not binding.

 

[Speedbird]

The pumps is where ever they sent it.
I hate not being able to take something apart and fiddle with it. (It's a new, mysterious thing)
I'm glad people don't think I bought too big a carb. I've always been under the impression is "hard" to do that.
At least not from a functional stand point. Performance maybe.
I'll go look at the secondary to see if the plates are sticking.
It's all an Edlebrock designed thing. Gasket etc.
One would not suspect a new carb with something sticking. What was the "fix"?
I put a timing light back on it for total after vacuum advance and it was OK in the 30s.
But I'll recheck it at idle which is also a very good idea.
I wound up using an M3872. The box.

 

[gtxrt]

the cable will have slop but make sure the choke is wide open and you are not just a hair on the high idle. again check the carb gasket.

 

[turbine68rt]

Try switching the vac advance from manifold to ported.

 

[Darter6]

The problem I have had is the Performer spread bore intake.
Using the Edelbrock thick base gasket the thin pattern of the intake using a AFB/AVS it may not be centered right causing a slight Vacuum leak.
I had this happen several times over the years. Just a thought.
It may sound like a silly question but did you install the plug fitting at the rear of the carb ?

 

[AR67GTX]

When you back the idle screw off is the tang on the primary shaft following the screw tip or is it hanging open? If hanging open, are you then winging the throttle and it’s dropping down and the motor dying? Or is it just snapping shut suddenly and dying on its own? You have enough return spring on it that it should be closing on its own but sometimes the shafts or plates are prone to sticking. I have a fully restored AFB on my GTX and it’s hanging a little high when I idle up to a stoplight or other stop.

 

[gtxrt]

I always run this plate. with the spread bore intake.

 

[Speedbird]

I've got one of those plates. Never been used and not even sure when I got it. Or why.
Yep. All plugs in.
I'll go back and check for vacuum leaks. That's a real thing. I'll use a gauge too.
I'm using the thin gasket that came with the cab. Everything fitted up as designed?
I went out and ran it again till hot. Secondary plates appear closed.

Again, what is happing is that I get a "good" idle with the linkage screw and when I rev the engine it doesn't go back to the idle speed I've set.
It stays faster and IF I turn the linkage screw to bring the idle back down, it comes down and wants to die.
Another thing I tried (again) was I trimmed the idle screws down to "closed" and set to idle speed via the linkage screw.
Not good but it idled. And when I then just cracked the blades it popped.
I assume it was running on the "off idle" ports?
I'm willing to accept that the carb is too big or I've got another problem, but I asked before buying it and the guy at Edlebrock didn't think it was too big.
My bad then.
This is the intake.
https://www.edelbrock.com/performer...1958-1979-chrysler-b-series-engines-2186.html

 

[oldbee]

If you took the mixture screws to “close” and it still ran, I’m betting on a vacuum leak somewhere. Maybe change base gasket?

 

[493 Mike]

The 800 size is fine. Use your timing light to check that advance (both) are coming back to base idle speed. The primary plates may be causing the vacuum advance port to be exposed. Sometimes not enough air is flowing to archive the desired idle speed and opening the plates to get that flow will expose the vacuum port. Perhaps the rear plates can be adjusted to open a little bit to achieve your desired speed with the primary plates closed enough to cover the vacuum port. And as mentioned, ensure the distributor mechanical advance is free and lightly lubed.
Mike

 

[Sam69sat]

You could try disconnecting the accelerator pump rod. Possible the pump is binding and not allowing the throttle plates to close completely. Just don't drop the little clip!

 

[Orig69]

I've got one of those plates. Never been used and not even sure when I got it. Or why.
Yep. All plugs in.
I'll go back and check for vacuum leaks. That's a real thing. I'll use a gauge too.
I'm using the thin gasket that came with the cab. Everything fitted up as designed?
This is the intake.
https://www.edelbrock.com/performer...1958-1979-chrysler-b-series-engines-2186.html

So you installed a square bore carburetor onto a spread bore intake manifold with one thin gasket.

If you install the seal plate and 2 gaskets (shown in post #12) the engine will run better than it does now.

 

[steve340]

I would fit the plate as advised. It is there to ensure there is no vacuum leak due to the flange shape of the performer carb flange.
My Performer intake manifold included one supplied by Edelbrock in the box.

 

[gtxrt]

what is your idle speed in park ? how far are your mixture screws out ? what cam are you running ? what is your base timing at idle with the vacuum advance not plug in. ? it must be a 4-speed car.

 

[Speedbird]

I wish I could could answer.
This aftermarket tach was supposed to be my guide.
Not working. That is another battle later maybe. Don't know if it's worth the trouble to pull the dash apart.
The cam was picked by the engine builder. It's not radical.
I think I set it at 8 degrees with vacuum plugged.
It's at 32 or so all in.
Our resident Guru built the distributor. So I'm sure no issue there.
I can alway go back to a Q Jet.
Seems a shame.