I fly mine with a GMS .76 and a Graupner 11x8 Pusher Prop.

Initially I too was having overheating issues as the cylinder head is not in the air blast when the engine is running on the ground.

A laser temperature guage helped immensly.

I noted that the head temp at the plug was exceeding 380 degrees F which is MUCH higher than what I should see.

So I adjusted the high end needle richer until the head temp dropped to 280-300 degrees F which was perfect.

This is one of those things where no amount of listening or taching the engine will help. I would not have thought of it if it wasn't for a friend who offered the use of his laser thermometer. After the very first reading I know what was wrong, and within a few minutes I had the engine operating as it should.

I'd suggest doing the same.