I would try two things first:

1. Make sure the air outlet hole in the engine cowl is about three times the area of the inlet hole. I tend to cut the bottom out of the cowls to make sure there is enough airflow over the engine.

2. Check for air bubbles in the fuel line at full throttle. This can be due to the fuel tank touching the plane and the transmitted vibrations from the engine frothing the fuel. The air in the fuel causes a weak mixture and can be difficult to detect. Can indirectly cause overheating.

Both these things will be important issues with a new and still fairly "tight" engine.