hello all i have a 2000 sportsman 90 that has an issue i cant figure out. when the bike is running and idling all is fine but as soon as you apply power it stars poping like its coming out of gear. replaced the chain, front sprocket, drive belt, checked rear sprocket bolts , removed gearbox cover and checked bearings and gears all good. is the problem with the clutch or the clutch cover??? not sure ant ideas would be greatly appreciated Charles D.