On the 250EX, you don't have to mess with the timing to rebuild the top end. The 250EX is a push rod engine, with the cam in the bottom of the engine.
Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!
You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.