i have a 82 xr500 with a new piston 2 sizes bigger, kn style air filter and the inside taken out of the exuhast. it is like 85-90 degrees outside and when i ride up hill for like 15 min the engine seises and the tire locks up. if i pull the clutch in for a few seconds i can pop it out and the bike restarts. i am worried it is over heating mabey too lean, could that cause this? i only have approx 150 mi new piston.