I have a 2000 z120 snowmobile,last week the chain kept on falling off....I put it back on and adjusted the tension...It seems that the clutch moves back and forth and is possibly knocking off the chain....has anyone encountered this problem????is it a broken clutch????should I buy a new one?????how can I solve this problem???? My son wants to race the snowmobile and I do not want to have the chain fall off.......any suggestions?????