As the message title refers to I have a 1989 KDX 200 Dirt Bike but not just one i have another. MY bike runs perfect but my other bike doesn't run right. When u hit the powerband in the top end it misfires and it never reaches full throttle but stays in the powerband if u let off the gas some. I have experimented and i shut off the gas petcock and rode around for a little and then when i got on the gas it hit full throttle every gear i shifted into until it ran out of gas. But then i decided to run with the gas petcock on and it started misfiring right as soon as i tired to hit full throttle in acceleration. I'M STUMPED AS TO WHY IT DOES THIS!!!! I DUNNO WHAT TO DO ABOUT IT! I think the main jet is too rich but haven't decided to lean it out because i wanted to ask u peoples opinions on what to do! For everybody who views this I ask ur opinion on what to do to cure this problem. Ur time is greatly appreciated!!!! Thanx!