I have an 86 camaro z28 with 305 motor that everytime i try to drive it down the road repeadly backfires through carb. When idling in neutral runs fine no backfire. I have replaced distributor cap, rotor, spark plugs, wires and i am at a loss. Any help would be great. Thanks

 

have you checked the timing?

 

Prolly not the timing. Basically that problem never is.

More likely, not enough fuel.

Changed the fuel filter?

 

also..did you go with exact same plugs for replacement? the 305 doesn't like a hotter plug than came factory is why i ask. if you put a hotter plug in it may cause a backfire also.

 

I would concur with a fuel issue at the carb, or some other problem with the fueling. Banging out the intake is usually caused by a lean, slow burning mixture that's still in the process of burning when the intake valve opens for the next intake stroke. That then sets off all the fuel in the intake, causing a backfire through the carb. In this case plugs shouldn't have that much effect. Since it runs ok at idle, the timing is probably ok and the problem is likely elsewhere.

 

If this helps any i adjusted the valves may have went to far down on cam but there is no obvious tick coming from valves. It has a new fuel pump but it had been sitting a few yrs but i pumped all the old bad gas out. Last time i tried to drive down the road it backfired alot through carb and cut off and couldnt get started again.

 

mine pops through throttle body, I might have a worn lobe or two on my cam?!?!

 

Or, a fueling problem; low fuel pressure, clogged filter, dirty injector, etc.

I'd start my investigation there, before messing with a cam.

 

i bought new accel injectors 21 lbs, cold air intake, k&n air filter, checked my fuel pressure 47 lbs at rail, new fuel pump, new fuel filter, holley adjustable fuel pressure regulator,new temp sensor, electronic temp control, throttle pos sensor, new iac, new cap, plugs, wires, new mass air sensor.