Just thinking out loud here. Is there a chance the battery is low? The only reason I asked is mine has a one wire charging system on it that does not charge at idle. As soon as I rap the throttle I get an instant spike in the amp gauge. I didn't know if there was any way a voltage drop or spike might rob or add enough power from the ignition to create the pop? For chits and giggles I'd unhook the alternator and make sure it isn't in that part of the electrical system. more