I haven't done too much with the motors yet but one problem I've noticed on the Sachs that I have running. Check your fuel flow. Specifically, remove the float cover and make sure the orfice is clear. If you have not cleaned the inside of your tank, you maybe getting a partical buildup. I had one that would run for 10 minutes, then die. If you ran the primery consantly, the motor would run. The other bike ran perfect for one tank of gas, then wouldn't fire at all. Both looked like they were getting fuel, but apparently not enough. I ran a paper clip through the gas inlet on the float cover and now both run fine.