I have owned my 250 Rebel for almost 1 yr now, and I am having a problem that I canĀ“t pinpoint. I have lost all my top end (mph wise). I can be cruising along at 65-70 mph and hit a hill and it drops off to 40-45 mph with the throttle wide open. I was told that the vaccum piston had a hole in it causing the problem, but when I replaced the vaccum piston it had no affect on how the bike runs. I have adjusted the valves, replaced the spark plugs & air filter, still with no results on how the bike runs. Before the problem started the bike would accelerate to 80-85 and hold the speed with no problem. Do you have any suggestions?