Heres what I have. I have a 1991 Camaro RS with a 355. 10.5 to 1 compression. I have old truck casting heads. 60cc with 2.02/1.60 valves. I have a comp cams cam with .507/.507 lift and 234 duration. I am running a high rise single plain intake topped with a Holley 670 Street Avenger vacuum secondary carb. Also ignition is HEI distributor with a MSD 6AL box and a Accell supper coil.

Here are my problems.

- Car will not start without pumping the throttle.
- Car will not idle at all. Runs for 3-6 seconds at about 1500 - 2000 rpm and then dies. Dosen't like to restart.
- If I keep pumping the throttlelightly the car will stay running barely and sound weak. It won't rev over 3000.
- It backfire through the carb to the tune of 2 or 3 feet of fire!! Exact same symptoms with a Holley 750 DP I used. Never ran.

Here's what I have done.

- As perviously stated, I've tried two different carbs. No difference.
- For future reference, all these had no change.
- Changed out coil for stocker.
- Replaced all plugs and wires.
- Checked MSD box and saw very good spark.
- Checked fuel pressure, pump in tank good, regulator functioning perfectly.
- Replaced intake gaskets, no vacuum leaks.
- Checked firing order. Even tried the alternate order just for FUN !!

Here's what I am going to do.

-Shoot myself if I can't fix this. I have been on it for about a month now!
- Break the 95' Z-28 I just finished doing a tune-up on for my friend because it runs perfectly! Damn LT-1!!!!

 

Giant vacuum leak (such as brake booster)?

Inspect for broken valve springs?

Make sure all valves are moving equally, especially exhausts?

Next, time for a compression check.

 

When checking fuel pressure did you check volume?

My car had same sounding problem. Could have bad pump or clogged fuel filter. Even tho good fuel pressure it may not have proper volume

Check your specs but normally you must take out the filter and put in a fuel pressure/volume gauge and bleed gas into a canister for a set time limit then measure the results.

Hope this helps narrow the problem!

 

almost sounds timing related?

 

i would really check the timing---maybe your 180 out

 

Yea, I'd lean toward timing being too quick or just way off, over tightend rockers, too much fuel.

 

I had a diesel a few weeks ago do the exact same thing. Didn't like to stay running. When the intake tube was pulled off, it was blowing exhaust out the intake like a burnt valve.

Found the problem was a plugged catalytic converter.

Drop the exhaust off your manifolds/headers and see if it runs any better.

 

yea chances are that its timing. i had the same prob with a 305. it was back firing thru the carb causing some wicked flames. i just pulled the disty, turned it 180 and dropped it back in and rotated it back and forth till it'll stay running. then fine time it with a light.

 

Always been my experience that backfire through carb = timing 180 out -- more often then not