Need more info. Does the engine backfire regularly, or irregularly? Did you have this problem prior to replacing the ignition? What shape are the valves in? Is the backlash set correctly? Many conditions can cause this problem, anything from the drive mechanism for the valve train, thru the valve train, to the valve seats, distributor drive, gaskets, springs, each having it&#039;s own unique symptom, some are common, but they can be isolated. It is unusual that I find a carburator as the source of a backfire problem, but it does happen. When exactly does it backfire? All the time? Under load? acceleration? Deceleration? Moving? Not moving? Idling? When it is being shut off?