My son’s engine is kicking my butt. He’s deployed to Afghanistan and I’m trying to restore his 1969 camaro. Bottom line, I have it running much better, but cannot fine tune it to stop backfiring out the carb with rapid acceleration off idle.

It has a 454,

- new summit racing 750 carb (plus used backup carb to troubleshoot)
- verified it squirts gas right off idle.
- new HEI ignition
- swapped out power wire to HEI, now have a relay giving 30 amp direct power from battery. Definitely good.
- plug wires are not swapped, must have checked 10 times. Even ran it at night looking for wild spark.
- new summit racing multi-spark box
- new summit racing dual plane intake. Plus swapped in a performer RPM intake to see if it was bad intake or intake to head seal
- new aluminum heads
- new hyd lifter cam/roller rockers. Broke in w/lube at 2000 rpm for 30 min. They pump fine, though I’m surprised how noisy the roller rockers are. Not crazy loud, just shocked you can hear the little devils. I adjusted at least 5 times, they open/close.
- New tall valve covers – no issue with rocker clearance
- plugged pcv valve line and power brake line. 20 vacuum at idle.

Played with timing, just
Played with idle mixture

This thing runs strong, sound bad *** at idle. But pops “sometimes” off idle when gunning it. Need to fix the header leaks, have tried multiple gasket combinations and spray copper seal even still leaks – but didn’t when I took it apart – sux!

Hate to pay somebody to fix this. Wish I could find out what is wrong, feel like a 16 year old chasing my first hard discrepancy. IF ANYONE HAS SOME GOOD TROUBLESHOOTING TECHNIQUES…

 

How are you adjusting the rockers? A friend on mine just got rid of his summit box he went through 2 or three of them till he finally got fed up and went to the msd. Did the back up carb make a difference?

 

I might do the same, though I'm unsure some minor noise could cause this gripe. I'm hoping to get the engine reliable, then fix noise/header leaks. I even pulled the timing chain cover and double checked that lined it up correctly. starting to seriously second guess myself - hate that!

 

Are you sure the advance/retard is working in the distributor, also try resetting the timing by slightly turning the dist. until it stops, then just try and totally bypass the ignition box and see if any of that helps.

 

vacuum gauge was bad, only pulling 5-8 psi. played with timing, runs better way advanced, but still not good. have to figure out why vacuum is excessivle low. damn, prefer to troubleshoot anything but vacuum!

 

A hot cam will give low vacuum reading at idle. Make sure the rockers are propely adjusted, an intake valve not closing properly will cause back fire in the intake system.