I didnt read the whole thing but basically tune and driving smooth is best run time. What gives you good run time is a perfectly tuned top needle on the carb, normaly leaning the top will give you mileage but you want to run at a safe/good tune with great power band. Also a good tunned pipe that is specified for that engine will help. If your pinned when you crash for a marsahl and just hit full throttle every turn then that will effect mileage to. I dont see clutches being a factor unless they are tired and slip.