RE: Engine cooling with cowl aircraft
What fuel and what plug are you using? Also, where is your tank?
I have my 120AX under a Yak cowl as well; didn't pay much attention to the "3:1" ratio, but I do have a hole the size of the engine head cut out over the engine so most of the air should escape there.
I had problems with over heating on another engine - the problem was that the engine was leaning out in flight due to problems with the fuel system and the engine not pulling enough fuel through the lines. It checked out fine on the ground and was difficult to diagnose because of that.
I use 10% nitro most of the time, and a #8 plug, sometimes a cooler plug on hot days. It makes a difference.