if its a 2 speed maybe the one way bearing instide the spur gear went bad, look and see if the spur gear is spinning when its not moving. make sure all your drivetrain drive cup universals grub screws are tight. If your overheating your either running too lean or you have an air leak on the engine, carb, fuel like or fuel tank. If your running too rich is wont overheat unless its sucking in air from somewhere else.