Carbs, why is lean hot?

[rdonahue@holli.com (Robert J. Donahue)]

While on the topic of carbs, I always wondered why a lean mixture makes an
engine run hot. Anybody out there have a good theory? Could it have anything 
to do with the evaporation of unburned gas? A friend of mine says air cooled 
engines are run extra rich to help keep them cool, fact or fiction?

Bob Donahue, Still Stuck in the '50s          
rdonahue@holli.com          
53 MG-TD #17639 under DIY restoration, NEMGTR #11470
71 MGB still in shop, 17 months and counting