I'd run a simple test:
Remove the main blades, install a fresh battery pack, turn on TX, arm AXE CP. Advance the throttle about 1/2 way, motor should have a consistant tone/hum, flip IDLE-UP switch, you should hear RPM increase, you should also see it in the head. If RPM increases/deceases with the IDLE-UP switch, then the motor is operating correctly.

How many hours are on this motor? Have you modified the Heat-Sink that covers cooling holes on the motor yet? You could have TOASTED BRUSHES! Under a NO-LOAD condition, does the motor get HOT, after only a few minutes of running?
You didn't say in your post if your using the stock NiMH battery, are you? You could have a bad cell, fully charge the battery & check the voltage with a voltmeter, you should have at least 10.8 vdc.

Shadow