for those of you who have not run pusher engines before, you need to keep your ground running to a minimum, because there is no prop blast blowing cooling air over the engine, they will over heat. If you have to do some running on the ground, throw a tractor prop the same size on, do your tuning, then switch the props back when you are ready to fly.
Also keep the engine fairly rich...the excess fuel and oil help carry heat away from the engine when it is running..If you feel you need to tweak it to get every last RPM out of it, your engine is too small..go for more cu in, and run it a bit rich....if they lean out in the air, it will overheat quickly...Again, no prop blast over the cylinder... If the cooling demands are more than relative airflow can disappate, the engine heats up...