I picked up this HT75 for $80 in need of a new carb (jets were missing/in bad shape). Put on a new carb and it got it running! The sprocket was about dead so I got a new one and figured out how to get old one off and now I am having problems with the screw to get it back on. It is reverse threaded and there were 3-4 washers on there as well. Best I have been able to do so far is get sprocket to spin with no chain attached but as soon as any kind of resistance is added the sprocket will stop. I have tried grabbing the sprocket with vice grips but the washers still seem to spin and won't let the screw fully tighten down. Any advice?