What do you have the timing set at? If you got it cranked up that will heat things up.
Edit: The only effect dust will have is on the bearings. Dusty conditions with the decreased traction that comes with it will provide less of a load on the motor. The only time this isn't true is if you've got the throttle pinned, doing donuts and the like with the tires looking like pizza cutters, for extended periods of time. That's a pretty high load, high rpm situation with very little airflow. It may be fun but also something that should be enjoyed in shorter bursts.
Anyway the the rotor is definitely toast after getting that hot, it loses magnetism after getting that hot and will only overheat even easier next time it's ran. The bearings are also a pain to replace in these motors. But the windings are probably ok. The solution is simple though, get a rebuild kit. It includes a new rotor and both end caps with new bearings installed for easy replacement. Make sure the timing is set to default (I'm unsure of exact value) and try again. Or get a big boy motor.
Last edited by Maj_Overdrive; 06-27-2016 at 02:32 PM.