Back firing and Missing Please help

[T_wilcox85]

Ok so here's the problem I have a 72 c10 with the factory 350, the motor has been rebuilt about 2 years ago or so. It has a HEI distributor and up until a week or so ago it was running great, but now its backfiring and missing. I checked the timing, firing order, changed the distributor cap and button, and i just put plugs and wires on it about 4 months ago. Anyways the back firing isnt really loud its kinda like a mild pop, and it pretty much chugs down the road. Anyways any help would be appreciated, Thanks.

[Wrenchbender Ret]

If it has a definit miss at idle you can pinpoint which cyl . it is by pulling plug wires one at a time. If it does not change when you pull a wire that would be the cyl. causing the problem. Use plastic pliers as that HEI throws a bolt of lightning & will get your attention if it bites you. If you narrow it down pull that plug & see if it has a buildup on it or is cracked. Pull the valve covers & make sure all the rocker arms are in place. Turn the engine over & watch that all the valves go up & down. I'm thinking you may have a bad camshaft.

[cdowns]

i'd double and triple check that the wires are in the correct positions on the cap and on the plugs

the bestest way to do that is remove all wires and install one at a time//lookin isnt accurate

[neba]

you dont mention if you changed the dist rotor. common problem on hei dist.

[Papa Smurf]

I recently had the exact same problem with my 72 c20 work truck. Try spraying some Berryman B-12, or similar, around the intake manifold. If there is a leak, it will pick up RPMs with the spray. Mine was leaking. Raplaced gaskets and torqued and it runs like a champ.

[OlMech]

Originally Posted by Wrenchbender Ret

If it has a definit miss at idle you can pinpoint which cyl . it is by pulling plug wires one at a time. If it does not change when you pull a wire that would be the cyl. causing the problem. Use plastic pliers as that HEI throws a bolt of lightning & will get your attention if it bites you. If you narrow it down pull that plug & see if it has a buildup on it or is cracked. Pull the valve covers & make sure all the rocker arms are in place. Turn the engine over & watch that all the valves go up & down. I'm thinking you may have a bad camshaft.

What happens when you floor it? If you get a "popopopop" through exhaut or intake it is a sure sign of something valve train related.. pulled stud, bent pushrod or bad cam/lifter.

[T_wilcox85]

ok so i havent had time to mess with anything until yesterday, its been crazy here close to christmas. But anyways I tried pin pointing where the miss was then it got cold out so i just bought all new plugs un-hooked all the wires and changed the plugs then went back with the same wires, apparently my carb is burning a little rich and i fouled a plug. So everything is back running just need to adjust my carb monday and i should be good i think. Thanks for all the help guys.