Ok, I have been through everything that I can think of and can't figure this out. I have developed a back fire/sputter through the carb. I am pretty sure it is something simple and nothing serious like a flat cam or a valve or spring issue but I could be wrong. It only does it intermittently. Very rarely does it happen below 4k rpm or so and once I really get on it then it happens every so often, sometimes more sometimes less. The noise in the carb is not a POP like a backfire but sounds more like air is being blown back out the carb with a momentary loss of power. I am thinking it is my coil or 6al box but not sure. Any help or suggestions would be great. Thanks.