My son's 150 R is cutting out at high rpms in all gears. I would say at about 80% throttle. I thought maybe a dirty MAIN jet but the carb and tank have been pulled and cleaned. The jetting has been good although the last race was > 90 F. Now considering valves which we will check specs on tonight. Could this be valves floating from poor springs.? The bike has about 100 hours on it. He races desert minis. Any other routine race maintenence advice (piston, rings, head, etc) would be appreciated.