I have a used gt3100 that was not kicking in the pto very well (very weak mower blade spinning). I decided to change pto belts as they were pretty loose. I replaced and it started great with strong mower blade rotation but 10 seconds later I saw smoke and shreds of belt flying out. Somehow the front belt came off the tensioner pulley and pinched. Before I put on another belt, any ideas? I'm fairly handy but not experienced in engines or tractors. I did notice the tensioner pulley did not freely spin too well. Thanks!