My 1996 XLT 600 is running terribly. It runs great up to 3/4 throttle then anything from 3/4 to full throttle it bogs or sputters. Its like it hits a wall. Does anybody know what this could be? It was running great a week ago. Also I can only get it up to around 65 miles per hour. I think it should be able to go faster. Only 400 kms on a fresh rebuild.