it's an 86 vt500. when you run it for a little bit and turn it off, it won't start back up. it back fires some times when it is trying. it's got striaght pipes and it looks like some one has been in the carbs. i checked the spark plugs and they aren't fouled out and the air filter looks to be in good shape. it never loses spark. could it be a temp. sensor or heat thing?