ive had the same problem today where the screw is jammed, dont keep attacking the screw other wise it will end in tears, simple take off the throttle housing put it in a vice heat the aluminum housing up around the screw with a blow torch for about 5 mins and it will come out really easy, if it wont go just heat it more, once its out cut the grove in the screw slightly deeper and re use it but put grease on the thread.