Ed Smith,
You are absoutly correct, the issue is temp, not richness, Bravo!

In general, the richer they are, the cooler they run. Obviously this can be changed with prop load, blocking off cooling etc... The average sport modeler that breaks in his ABC type engine in a slobbery rich method with the same prop he'll fly with is more than likely going to be running it way to cold for the design fit to be achieved. In this manner, too rich equals too cold and too slow.