It only has this problem after it has warmed up. It runs great for a few minutes and I have power and speed, but after about 5 minutes all of a sudden it starts to go real slow and has no power going up hills. If I don’t keep the throttle open it dies. The fuel tank is not rusty, the fuel flow is sufficient, the belt is not slipping, however the muffler seems to get pretty hot. If it was a muffler problem, wouldn’t it run crappy right from a cold start? Or would the carbon heat up and expand or something? I would just run it without the muffler for a few days (just to get me to school and back,) but I am afraid of damaging the engine. Could that happen?