I have no idea what is wrong with my sled... here is what it is doing.....when I am ready to ride I start it up and let it warm up for about 5 min. than I go out and ride. No more than five minutes after riding the sled begins to bog down past about half throttle, also there is a lot of backfiring and smoke coming out of the exhaust, I can barely get any speed out of it to make it move. when I lift the track up off the ground and hit the throttle it acts as though nothing is wrong but as soo as i get back on and ride the same problem occurs again. If anyone has any suggestion on how to fix this it would be greatly appreciated.