Been there, frequently. No damage. That's my point?

Maybe we're talking different conditions though? To me, a "carboned up" engine is very likely going to have a stuck ring and heavy ash deposits on the top of the piston and head? Noticeable carbon build up on it's spark plug (not just black), with a history of fouled plugs? Carboned up to the degree the performance of the engine is degraded?

When I think "rich engine", I'm not talking slobbery rich to the point it's missing badly trying to clear itself out on it's entire take off run and while at cruise speeds. I'm talking about an engine I would fly without hesitation. The rich engine I'm talking about is one that might be burbling in mid range, rpm set rich of max when set on the ground, unsteady idle, but good response? Mine are run this way frequently (especially when the weather has taken a turn to the warmer) - and there is no carbon build up. That's one of the bigger reasons I run a quality oil? Yes, oil needs to lube and cool, but it can't be causing/allowing carbon buildup either? -Al