Check rpm, over revving will cause running hot. Check mixture, running lean will run hot. Check fins and fan function, needs air flow to cool the head and barrel.
Fins not clogged, will have another look at the fan. Not sure about the over-revving, by the way how are you checking the rpms, with a tachometer?
By mixture Dieselboy probably mean carburetor adjustment.
As for RPMs yes it is done with a tach and not how far it throws a rock at a Roo. Just make sure you tach is set for one pulse per rev and not dividing 2 or more as some tachs can be set to do.
