I agree with randay. As long as the engine is running well, I try to make sure it's in the 240-260F range. Less than 240 and I would say I'm running too rich. More than 260 and it should begin to sound too lean. 300+ is bad, although the CRF can handle 300+ without blowing up on you or burning plugs in 4-5 minute heats.

BTW ... I am by no means advocating running a CRF at 300+ degrees.