I HAVE A CHEVY 350 I HAVE REBIULD ABOUT 10,000 MILES AGO, BACK TO STOCK. BESIDE THE HOLLEY CARB I BOUGHT BRAND NEW. I PUT IT IN THE TRUCK IT RAN GREAT!!! NOW I AM DRIVING DOWN THE ROAD ABOUT ABOUT 2600 RPM, AND IT WILL START BACKFIRING IN THE CARB. SO I TOOK THE CARB APART AND CLEANED IT ALL UP. I PUT IT BACK ON THE TRUCK AND NOW IT IS BACK FIRING MORE AND AT LOWER RPM. I HAVE TAKIN THE CAP OFF AND IT LOOKED BRAND NEW NO PROBLEMS. I HAVE NO CLUE WHAT IT IS. HELP?????:noway:

Could be a burned valve or timing chain problem. Do a compression test and leak-down test to verify the health of the engine.

or it could be you're losing a lobe on the cam.

FYI, backfiring thru the carb is almost never caused by a problem in the carb itself.

What part of Az are you in?

And, all caps are not favored, hard to read.

1. Intake valve doesn't seal (burned, bent, bad seat, broken valve spring, valve stuck in guide.)

2. Exhaust valve doesn't open (bad cam lobe, bent pushrod, broken rocker arm)

My first thoughts are mentioned above. What about your ignition? Wires, cap, rotor etc in good shape? Could be ignition cross fire.

I have checked the wires and the rotor and all the ignition stuff I have a msd 6a on it too, it all looks good. I am going to try the compression test and see what is going on. The truck runs about 2800- 3000 rpm on the highway when drivin. It is just a tow truck for a race car, but i do live in Arizona with high heat, so i don't know if that has done some damage. And Tom I live in gilbert, east mesa.