Car falls on it's face when accelerating, 355sbc w/carb '71Camaro - Team Camaro Tech
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post #1 of 11 (permalink) Old May 1st, 09, 04:22 AM Thread Starter
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Car falls on it's face when accelerating, 355sbc w/carb '71Camaro

I just got my new combo together and got my car running. It's a 355sbc with afr 180 heads, voodoo 268 cam, perfomer rpm air gap intake, headers, 9.9:1 compression, the usuaul 350 sbc type of build up. The problem I'm having is that under acceleration, the faster I put my foot to the floor, the worse, the car falls on it's face then finally kicks in(Once it kicks in it really gets up and goes!) but the "stumble" is pretty bad. I had the same problem with my older setup "different heads and cam/intake", never got it right then, "then decided to go with different heads/cam" but at that time I tried 2 different distributers, I had a mallory hei and I now have a stock HEI that came out of a friends ZZ4 crate motor which is brand new and he never used. I set the timing at about 12 ish degres with the vaccum off and if I remember correctly it's at about 32ish at 3200 rpm. The carb is a HOLLEY Street avenger 670. I tried the stock 31 acc pump nozzle and then tried a much larger one, I think it was a 39 or so, and tried 2 different springs in the secondaries. It is still doing the same thing, Throttle response is great when I rev it up in neutral and it all sounds healthy, but once under load accelerating, it is falling on it's face then kicking in. Any idea here on what to try??? I heard holley has a larger acc pump??? different acc pump cam??? Any ideas here??? Also, the combo is matched up with a 2800 coan converter and a gear so I know that's not what's holding it back
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post #2 of 11 (permalink) Old May 1st, 09, 08:10 AM
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Re: Car falls on it's face when accelerating, 355sbc w/carb '71Camaro

Use a vacuum gauge and adjust the mixture screws for the highest reading.
Add more initial advance.
Connect full time vacuum to the HEI vacuum cannister.
Might try another carb, not a street avenger model.
Manifold vacuum is ____?

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post #3 of 11 (permalink) Old May 1st, 09, 08:20 AM
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Re: Car falls on it's face when accelerating, 355sbc w/carb '71Camaro

Lock out the distributer!! 36 degrees total..are you sure your holding fuel pressure??
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post #4 of 11 (permalink) Old May 1st, 09, 09:44 AM
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Re: Car falls on it's face when accelerating, 355sbc w/carb '71Camaro

Your parts are fine, your problem is in the tune up. Have you recurved the distributor? Is 32 degrees of timing at 3,200 all of the advance or does it increase beyond that RPM?

Give it more initial timing and get the total timing up to 36 or 38. If all you have is 32 degrees, thats not enough. You should not need a larger accelerator pump. If increasing the timing doesn't fix it you could try a different pump cam. Have you checked the operation of the accelerator pump? If you move the throttle slightly the pump should squirt fuel. Check it off idle and at part throttle.

'69 Camaro - 429 SBC Dart Iron Eagle 9.325" block, Crower crank, Crower 6" billet rods, Ross pistons (10:1), Total Seal rings, AFR 245 heads, T&D steel body shaft rockers, Cloyes Timing set, custom ground 4-7 swap solid roller 274/286 @ .050" with .704" lift, Dart single plane, Holley Dominator EFI on E85, Injector Dynamics ID2000 Injectors, Stef's #1705R oil pan, F2 Procharger, Lemons 2" primary 4" collector, ATI 9" blower converter
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post #5 of 11 (permalink) Old May 1st, 09, 04:59 PM
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Re: Car falls on it's face when accelerating, 355sbc w/carb '71Camaro

Your problems are common and usually related to timing, and carb setup issues. Just go slow and do one thing at a time and observe the reaction to the change. In my case I added vacuum advance with an adjustable can, had to make adjustments to the base idle position (we'll save that one for later), adjusted the float levels. Adjusted the accellerator pump setup, and set the idle mixture using the peak vacuum method. All of these things helped make it run like it should.

Go to the home page and look for the tech reference series where you'll find some good carb 101 stuff https://www.camaros.net/

Timing and carb settings all affect one another which can be a tail chasing experience. That is why you want to take things one step at a time.

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post #6 of 11 (permalink) Old May 2nd, 09, 06:09 AM Thread Starter
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Re: Car falls on it's face when accelerating, 355sbc w/carb '71Camaro

Is there any way to adjust the curve on my HEI vaccum advance distributor, or any other adjustments that can be done on it??? Should I possibly get a different distributor?? Mechanical advance/different springs/weights??? I don't know much about distributors, but thinking this could be the problem???
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post #7 of 11 (permalink) Old May 2nd, 09, 10:19 AM
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Re: Car falls on it's face when accelerating, 355sbc w/carb '71Camaro

Here are several recurve kits available from Summit.

http://store.summitracing.com/egnsea...115+4294908216

Don't change distributors just recurve yours.

'69 Camaro - 429 SBC Dart Iron Eagle 9.325" block, Crower crank, Crower 6" billet rods, Ross pistons (10:1), Total Seal rings, AFR 245 heads, T&D steel body shaft rockers, Cloyes Timing set, custom ground 4-7 swap solid roller 274/286 @ .050" with .704" lift, Dart single plane, Holley Dominator EFI on E85, Injector Dynamics ID2000 Injectors, Stef's #1705R oil pan, F2 Procharger, Lemons 2" primary 4" collector, ATI 9" blower converter
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post #8 of 11 (permalink) Old May 2nd, 09, 11:19 AM Thread Starter
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Re: Car falls on it's face when accelerating, 355sbc w/carb '71Camaro

Okay, I tried several things, different acc. pump nozzles, a different acc. pump cam, went from a 65 to a 45 power valve, and put very light springs in the distributor and still the same problem. When accelerating very slowly up to speed it's fine, but when I hit the gas medium to fast the engine just looses all power for a few seconds, then kicks in and when it does, it is fast, but this weak spot is not going away. ??????????????????????????????
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post #9 of 11 (permalink) Old May 2nd, 09, 11:23 AM
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Re: Car falls on it's face when accelerating, 355sbc w/carb '71Camaro

Quote:
Originally Posted by camncars View Post
Okay, I tried several things, different acc. pump nozzles, a different acc. pump cam, went from a 65 to a 45 power valve, and put very light springs in the distributor and still the same problem. When accelerating very slowly up to speed it's fine, but when I hit the gas medium to fast the engine just looses all power for a few seconds, then kicks in and when it does, it is fast, but this weak spot is not going away. ??????????????????????????????
What is your total timing and did you check the accelerator pump operation off idle and at part throttle?

'69 Camaro - 429 SBC Dart Iron Eagle 9.325" block, Crower crank, Crower 6" billet rods, Ross pistons (10:1), Total Seal rings, AFR 245 heads, T&D steel body shaft rockers, Cloyes Timing set, custom ground 4-7 swap solid roller 274/286 @ .050" with .704" lift, Dart single plane, Holley Dominator EFI on E85, Injector Dynamics ID2000 Injectors, Stef's #1705R oil pan, F2 Procharger, Lemons 2" primary 4" collector, ATI 9" blower converter
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post #10 of 11 (permalink) Old May 4th, 09, 11:51 AM
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Re: Car falls on it's face when accelerating, 355sbc w/carb '71Camaro

I'll be curious to see what you come up with as far as the solution. I have the same setup as you, same intake, cam, headers, carb, 355 motor. I have Edelbrock RPM heads and a manual transmission.

My total timing is 36 and my initial is 18. I have a Pertronix setup. I have been the same route as you but have not made any progress. But now I can't seem to get the fast idle cam to stay down when I accelerate. After working with Holley Techs, they want me to send it back to them. I'll mention the flat spot on acceleration to see what they come up with while they have the carb.

Rick
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post #11 of 11 (permalink) Old May 31st, 09, 06:59 PM Thread Starter
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Re: Car falls on it's face when accelerating, 355sbc w/carb '71Camaro

Update: Bringing this post back from the dead. I have messed around with this holley carb for too long now, and just put on an Edelbrock 750 that I had laying around, and would you believe it, the car runs great now, I have no idea where the timing is set at this point, and haven't even tuned the carb one bit, I just put it on and it's a world of difference. I'm going to see where the timing is at and adjust it accordingly, throw a vaccum gauge on the carb and set it. I'm not quite getting full throttle, I have to adjust the linkage a bit, and once that's done, it should be perfect. Well, I'm done with the holley carb and glad, what a waste of money!!! Now I can get some other things squared away on the car and just enjoy it.
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