Common problem. It could be ground wire, or switch, or cdi. Often times if it's the switch you can turn it off very slowly and it will shut off at about 3/4+ rotation. Sometimes it's the ground from the cdi corroded and not making good contact so that you get intermittent shut offs. Other times it's the cdi itself which will usually show up as not shut off when cold but after warm up and fan cycles through on and off the machine will then shut down as it's supposed to. You just have to try and eliminate the easy stuff first (ie. grounds and switch) and go from there.