1978 Ford 300 backfire/popping
 

I have a problem with my truck. Its a 78 ford f250 with a straight 6 300. Not every time but most of time after truck has been running for a while it will backfire, or pop after i shut her off. Does not make a loud noise out of exhaust, just in engine. I replaced, plugs, plug wires, dist cap. Any ideas on how to fix it?

Is your truck trying to run on after you turn the key to off???
This is usually caused by high cylinder temps, caused by EGR not working or carb running lean. Idle set too high will contribute also.

yeah, after i turn the key, it still wants to run

Make sure your solenoid ain't still bumping the starter to turn over the engine. Your carb may need to be reset...carry to a mechanic if you cant set carbs good.