Driving down the high way today, adn I have a small miss of sorts. Cruise rpm is 3100. Well, when I'm at a steady cruise it nisses a little. Also, when it misses there's a small puff of white smoke out the passenger side exhaust pipe. But when I put my foot into it a little, it clears up and runs smooth as can be, pulling like a freight train untill I grab the next gear. Where would you start looking? Bad plug or wire? Carb issue? My timing is at 15 initial with 36 total all in by 2500, so that's not an issue. I'm figuring the small puff of smoke is the air/fuel charge that didn't get burnt when the ignition didn't fire in the hole it's coming from. IDK, any thoughts?