Start it and let it warm up. with the engine running remove one plug wire at a time. rev engine when you remove a wire and the backfiring quits you have isolated the offending cyl. Check that cyl real good for weak valve springs or bad cam lobe bad valves. My son had a 351 winsor that popped really bad pulled the heads and every exhaust valve was burnt. if you dont have sucess with isloating by the one wire at a time method. do a compression check. If compression is good. check coil condenser and carb. There aint a piece of cast iron in the world that can fool you unless you let it. OldWolf
HI: I know this sounds stupid, but check voltage at ballast (he said he had points) just went through this with a friends car , had 3.2 volts to the coil, new ballast, runs perfect, would not pull a sick whore off a toilet seat before. Chris
I agree with this - made quite a bit of money back in the 80's and 90's changing small block chevy cams with flat lobes . . . they ran just like you describe.
...If this was said already disregard.....check to see if the vacume can is working on the distrubitor,.....check to see if the carb squirts gas down into the carb when the engine is off by working the linkage.....check to see if the points are bouncing...my nephew had a NEW point set and it was missing the metal spring, he put them it not knowing ,and the motor would run great at idle and would run like hell when he tried to move it.....Miller
just bought a 60 chevy with a 283. car had the same problem breaking up, popping through carb under load etc. After setting dwell at 30, doing the entire dance problem still present. found the previouse owner had the positive side of coil running to the distributor ! ! ! swapped the wires and bingo ! Just sayin in case you replaced the coil recently ! ! not saying you are stupid , just an honest mistake guys make.
I've had that same problem. I thought that was an only me thing. If the distributer gear is worn or if the lower bushing is loose you can come up with the same type of problems. I doubt that gurl is the problem, you are dating a gurl right? Unless, well have you noticed a black cloud over her head?
Lots of good suggestions here. Hope you find something simple (cheap!). Small blocks with flat cams...that was an issue from around late 74 through early 80 in 305s and 350s. The rumor was that the General tried to heat treat too many cams at once and they all ended up soft. Sadly it took about 40K+ miles to show up. YOU know your motor better than any of us. Is there just one bit of info we ain't gettin? Did ya whizz it up in the last few months? Miss a gear? Throttle stick open? I'm leaning toward a mechanical problem vs a tuning problem only because you say it's been good for a while. Bent pushrod, broken spring, bent valve because you tossed em for a few seconds, doesn't take much. If it is all OEM internals and it's an oldie (has to be...283) then I'm thinkin that's your direction. And it'll be cheaper to fix than your truck.
I had the wire from the distributor to the coil get pinched under the cap. It started grounding out after a while causing backfiring while under load and kept getting worse as time went on. I tries everything that was suggested above before I figured it out.
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