Run a fuel with Castor oil and Synthetic oil (Power Master, Omega). I wouldn't recommend using a full synthetic fuel like Cool Power to break in a new motor. Synthetic fuel is clean burning, but the oil breaks down at a lower temp than castor oil. If you run your engine lean by accident, the small amount of castor in your fuel will withstand a higher temp than the synthetic.

General rule of thumb:
High nitro fuels need a colder plug and,
Lower nitro fuels need a hotter plug.