1967 JD 1020 runs great for about an hour. Then it occasionally tries, sometimes successfully to stop running as if the key was turned off. It does not miss, it just tries to die or it does die. When this happens, it seems to be associated with the tractor bouncing or moving abruptly on rough terrain. Eventually it will do it on smooth terrain. It is very intermittent. I did have a continuity issue with power to the ignition (bad wire) but that has been fixed and the carb was overhauled not long ago. My thought is the Governor is misbehaving. The tractor runs great until the moment this mystery occurs. If it dies, it starts up and runs fine until the next event. Any help is appreciated.