well im at my wits end here just need some advice. ive got a 69 c-10 with a 72' 350 (casting #3970010) 4-bolt mains. its a fairly low mileage motor somewhere around 50 thousand. its got heads with castings something like 339 im not sure i ran them once i thought they came back to be 1.72/.150 74.5cc chamb (garbage, i know) i ran it last summer with a stock intake and roch. carb. it sat over the winter and i ran it in the beginning of spring it was alright secondarys had froze up. i got a summit stage 3 alum highrise airgap intake and bought a used model 4150 650 double pump. got it all together and it ran but kinda junky. eventually after messing with the distributor, and repeated flooding, we got it right. i took it out and came on to it and it kind of just fell on its face and then popped and dies. ha dthe carb adjusted and it was running "ok" but then it started backfiring alot. ive adjusted the timing checked compression all cylinders at least 155psi most 160. adjusted my accelerator pump springs switched back to my old quadrajet and it still does it. so basically it starts, idles, runs ok up to, im guessing because i dont currently have a tach, 1800-2000RPM then starts backfiring sounds like a popcorn machine. im at a loss i dont know where to go from here help me  

Pull your plugs after idling awhile and try to on a low traffic road.Steady cruise as best you can,throw in neutral and shut it down fast and pull some plugs.Maybe check your distributor advance weights also sometimes they stick.Let us know    WIEDER  

Yeah, the backfiring means you've got an issue with your ignition system. You don't mention if it's an HEI unit or a points-type distributor. It could be a problem with the vacuum advance not functioning properly.

Sounds like either way, you need a distributor rebuild.  

thanks for the info, its an HEI by the way. i bought a new vacuum advance the other day, the one i had was bad but it still made no difference. a friend dropped of an whole used assembled distributor today so i think i may try a switch with all my new tune up parts and advance on this different shaft and hope for the best. I had a thought maybe the mechanical weights or the coil pick up but i figured it wouldnt run at all if the pickup was bad. ill prob do it tomorrow so ill let you guys know. thanks  

In responce to 69chevyC10. Sounds to me like your car ran fine till you put intake and 650cfm carb on. You may be over carbureting with more air flow and gas input. I put a 650 spreadbore holly on my stock v8 and it ran hesitant. I changed to a 500cfm edlebrock and it ran great. No hesitation. Bigger carb works better with larger valves (194/160)example.orgreater. PS;This may not be your problem as in my case.Nevertheless, I hope it might be most helpful.I am ignorant concerning high tech specs. When you get it solved,post your results. THANKS!!. I love older muscle cars Mine is 79Monte/Carlo.  

To 69chevyc10.Im Sorry,i meant truck