I liked the power it had for a short while with the stock motor but I can see that there is no way to maintain that level with a 300 motor. It's up against both rpm and current limits. I was pushing over 70watts into it. That's speed400 territory. I felt a 280BB might do the job for a little longer because of its bigger replaceable brushes but that's still pushing it.

I tried replacing the 300 motor with another slightly used spare and tested it on the bench. It burned the brushes before finishing one cycle on a freshly charged 720AAA NiMH Sanyo 8 cell pack. The design of the stock gearbox totally blocks all the motor vent holes which is probably letting the motor overheat.

So I replaced it next with a Permax 280BB motor. It's gone into a Graupner 3:1 FG3 gearbox. I Just needed to make up the beam motor mounts.  It just barely fits inside the cowl but it made it. The gearbox to firewall brackets are made from folded .032" aluminum sheet.