I have a trailmaster mid xrx go cart with 6.5 hp and when I hit the gas the clutch attached to engine opens and engages but the driver clutch in which chain attaches to does not open. The engine revs at high rpm but the cart bucks a little and than goes about 5mph. I can open clutch by hand. Spring seems good.I put cart on stands and when reved up driver clutch is not opening. Any suggestions. Could this be from worn belt?