back firing problem

[marklees]

i am racking my brains on this one, cleaned carb rebuilt mag,pulled head off cleaned valves. runs good till warmed up, then starts popping out of the carb and pipe especially when you put it under load? any ideas would be appreciated. thanks

[oliverchris]

Some kind of interruption in the fuel line is what seems to fit the symptoms? Is the fuel tank low or has it been low recently? Try blowing back up the line from the carb into the tank and see if it is easy or if anything appears in the tank...sometimes at idle a small piece of crud has little effect but when the flow is increased it can cause a blockage...
Good luck...

[440roadrunner]

Popping back through carb,  as an "even"  pop  from one cylinder,  might be flat (exhaust) cam lobe,  sticky/ burned valves,  or something in valve train causing valve to stick open.   You should be able to short one plug at a time to ground,  put under brief load,  and tell which cylinder(s)  are cause.   Have you run compression check?