Sounds to me like a brush problem. I've never changed brushes, so I couldn't tell you what to do.

What motor are you running? if it is a lower end motor ($20-$30), it might be easier to just pick up a new motor. If it is a higer end motor (Trinity D-6, etc...) You could benifit from new brushes, and possible a com turn. Most hobby shops will "Cut" the com for you (for a small fee).

You may be able to find info on changing brushes on Trinity's or Orions website...

Good luck.