Tried a new starter which was turning over the engine fine(150 cc) but I let it get too hot and it shut down . i took it out and now today i just set it up to run from the battery and it seems fine. My question is if it has a thermal type shut off till it cools down or can it die as far as starting goes but still run without the load. I was under the impression that an electric motor either ran or it didn't. Of coarse I could just have bolted it in for a try but I had to go to work.
Tim

 

I've never seen a thermal cutout in a starter motor.

Things expand when they get hot, and perhaps that thermal expansion is triggering an intermittent fault of some kind. Perhaps a turn gets shorted to ground when the armature expands, or something like that.

Also it may be worthwhile to take a look at the brushes and brush holders to make sure they are getting good connection to the commutator. Water inside the starter causes the positive brush holder to corrode which prevents the brush from being pushed up firmly against the commutator.

Warning: It's easy to take a starter motor apart, but getting it back together is tricky. I had to make a "C" clip out a piece of scrap steel with a string tied to it. The clip held the brushes in the end plate back enough to let me get the commutator partially inserted. Then I yanked to clip out before inserted the end plate the rest of the way.