Strange Behavior Of New AVS2

[66 Sat]

You need to take the lid off and set the float heights if you haven't yet. They get knocked around in transit and can be all over the shop.
Also they don't tolerate too much fuel pressure (5.5 psi) unless the floats are adjusted accordingly so that might be an issue too.

I'd pull it off the car and disassemble it, check everything looks good.

 

[lewtot184]

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

View attachment 1770462

This is a must on spread bore edelbrock intakes.

 

[BSB67]

Your symptoms sound like a vacuum leak. Idles high, then dies after trying to adjust it down.

After it is warmed up, when it is idling the best you can get it, cup your hand over the primary throttle bore opening in a fashion to choke it out. While doing this, if the idle speed increases before it dies, you have a vacuum leak.

 

[threewood]

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

View attachment 1770462

100%. You need the spacer or the secondaries will drag.

 

[BSB67]

100%. You need the spacer or the secondaries will drag.

You might need a spacer, but I don’t think the secondaries will drag.

 

[Geoff 2]

[1] Carb is NOT too big.
[2] Remove carb & make sure that all the passages/openings in the carb base are covered by the gasket.
[3] With the carb removed, check the following:
- float level [7/16"]
- remove boosters [4] & check that gaskets are correctly oriented. Blow passages with compressed air. Unlike a H, no gaskets neded if you are careful.
- check T slot position. At idle 0.020 - 0.060" should be showing below the blades. More than this, could be activating the vac adv unit [ causing your problem ]
- check t/blades for binding.
[4] These carbs will tolerate up to 10 psi of fuel pressure, but f/level will need to be adjusted [ see chart ].
[5] In 50 yrs of using AFB/AVS carbs, I have NEVER had to use the inner hole on the pump arm. You are just pumping in excess fuel. These carbs have a big 30 cc pump. Use the outer hole & re-adjust pump arm for correct plunger height.
[6] Refit carb & try. If problem still exists, disconnect & plug VA unit & PCV, in that order.
[7] 8* init timing is nowhere near enough idle timing. Would need more cam info to be exact, but 20-30* is probably going to be best.

 

[lewtot184]

The flat plate that is supplied with the manifold is to insure no vacuum leaks with a square bore carb on a spread bore manifold.

 

[Speedbird]

Its that time of the year here with temperature swings.
Cold and then warm moist swings in the weather.
Condensation on everything.
No painting today.
Maybe I can dive back into it and check the vacuum angle.

 

[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.

View attachment 1770454

Here's the info again from previous posts.
Everywhere on the internet still shows a spread bore which is what I wanted.
Edelbrock said that they did not make a spread bore anymore. Hence, I bought this carb to go with the intake.
Be aware. I'm sure some know this already.



I have installed the adaptor plate which I assume came with the Performer intake that I bought during the lockdown.
I was buying lots of things since one didn't know what would happen in the future in supply.
It seems to have some type of orifice adjacent to the secondaries which I assume caused it the problem.
But the gasket does appear to seal to the manifold without the plate.
Apparently not enough.



The problem seems to be gone and I can now move on to adjusting the carb.
Better vacuum.



In my defense, I just don't like square bores for my use over the years and have never run one.

I just bolted it on the manifold without looking. Duh.
Who knows if it would need the adaptor on a variety of square bore manifolds.
I'm guessing yes.
Thanks.

 

[Rishi]

Sweet. So you figured it out? In the end, what was the issue? Were the secondaries binding up on something or not? I was putting my money on that, and hope to win the pool. Just kidding. Well done.

 

[Speedbird]

No it was a vacuum problem.
Oh, I also moved the advance to ported which the instructions don't seem to indicate to do.
I read it as "manifold vacuum" because there is no EGR valve.
Caveat. I made two changes at the same time and the idle problem seems to be gone and there is better manifold vacuum readings on a brief test run.

 

[gtxrt]

No it was a vacuum problem.
Oh, I also moved the advance to ported which the instructions don't seem to indicate to do.
I read it as "manifold vacuum" because there is no EGR valve.
Caveat. I made two changes at the same time and the idle problem seems to be gone and there is better manifold vacuum readings on a brief test run.

your problem was not where the advance was hooked to if any thing moving the advance to ported would give you less vacuum at idle.

 

[turbine68rt]

In the Edelbrock video setup guide they advise using ported for distributor advance, and the manifold port if you use a vacuum modulator for non-Chrysler automatics.

 

[Houle #382]

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.


View attachment 1770403View attachment 1770404View attachment 1770405View attachment 1770406

The AVS2 carbs are a great carb, but I think the 800 is too much carb for the 383 in my own opinion it's easier to over carb than under carb. I have a 650 AVS2 on a mild built 440, I'm running a 600 lift hydraulic roller cam with 440 source aluminum heads, Edelbrock performer RPM intake, 650 AVS2, stock exhaust manifolds into a 2 1/2 inch H pipe into 3 inch Dyno Max super turbo mufflers and 3-inch tail pipes and tips. 4 speed with a dana rear with 3:54's. Timing is 12 degrees initial and 36 total at 2500 rpm. The only thing I did to the 650 was I changed the factory spring to the pink springs and changed the secondary jets to 104's from the .098's. The car flat out runs. I did try the 800 AVS2 but didn't like the performance, it always ran pig rich, I tried changing rods and jets but it did not run very good, it didn't like smaller jets or rods that's when I bought the 650 AVS2, best move I made. My car is a street car will probably never see the strip but the light to light acceleration with the 650 has it all over the 800. I actually ended up sending the 800 back to Summit got a full refund. Summit is the best to deal with.

 

[gtxrt]

The AVS2 carbs are a great carb, but I think the 800 is too much carb for the 383 in my own opinion it's easier to over carb than under carb. I have a 650 AVS2 on a mild built 440, I'm running a 600 lift hydraulic roller cam with 440 source aluminum heads, Edelbrock performer RPM intake, 650 AVS2, stock exhaust manifolds into a 2 1/2 inch H pipe into 3 inch Dyno Max super turbo mufflers and 3-inch tail pipes and tips. 4 speed with a dana rear with 3:54's. Timing is 12 degrees initial and 36 total at 2500 rpm. The only thing I did to the 650 was I changed the factory spring to the pink springs and changed the secondary jets to 104's from the .098's. The car flat out runs. I did try the 800 AVS2 but didn't like the performance, it always ran pig rich, I tried changing rods and jets but it did not run very good, it didn't like smaller jets or rods that's when I bought the 650 AVS2, best move I made. My car is a street car will probably never see the strip but the light to light acceleration with the 650 has it all over the 800. I actually ended up sending the 800 back to Summit got a full refund. Summit is the best to deal with.

something was wrong with that carb or the floats were off or too much fuel pressure. if speedbird didn't get down to the problem he would have said the carb was junk but it was user error not the carb. am running 2 800 avs2 one on a 440 RT small cam stock exhaust 3.23 gears and on a 4400 lb with me in it 67 Newport 440 217-221 duration 482 lift cam. stock exhaust with 2.94 gears car has instant throttle response and goes side ways off the line and gets 17 mpg on the highway all spark plugs are white with just a little color both carbs are jetted up one size on the primary and secondary and 1 to 2 sizes smaller on the cruise mode. both cars with iron heads and the Newport has even a 1.6 exhaust valve. we both told our stories more than once on different threads. not sure what happened with your carb.

 

[T Brashears]

I have that carb on a DP4B with a !" 4 hole plastic spacer,not over cammed 383. I had to slightly hone the bores of the spacer for throttle plate clearance. It's not as too big a carb for your engine as some will have you believe. On mine the floats were off outof the box,I borrowed a 650 AVS2 from a friend and those floats were spot on. Jetted the same by afr ,the 650 ran excellent,If I try to lean the primary in the 8oo,it gets a little lean surge at tip in that is easy to drive through unless I'm in rush hour traffic.Both carbs I tightened the air valve spring a little. The 800 seems to pull harder up top,and mileage was too close to matter.Car has 2500 converter and 3.73 at the moment.When I can get to a test n tune this year I'm taking both carbs,the winner stays on! The air valve let's the engine take what it wants.Remember 6 packs and multiple carbs on factory performance cars. Yeah,the perfect size carb for your car perfectly tuned is best,but not everybody is going to spend track time doing it.The 650 AVS2 has slightly smaller primaries which I think helps velocity off idle. I was a Q-Let lover way back,I'd have a thermoquad now if I could get a good one without a mortgage payment.

 

[gtxrt]

the annular boosters on the AVS2 were made for the off line hesitation. they do get plugged at times and just need take them off and clean them out with air.

 

[T Brashears]

I did all that,a wee bit more fuel fixed it.

 

[Orig69]

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.


View attachment 1770454

This picture shows the Edelbrock 650 CFM AVS2 carb and it's still a square bore.

 

[T Brashears]

I had one in my hands and on my car,and it may go back on. The primaries are smaller than the secondaries by a small amount,but still a square. Spread bores are a small primary with a very large secondary necessitating the need to widen the rear of the throttle plate and manifold.