If it's getting very hot and noisy then the first thing to check is that it's got plenty of fresh, clean oil of the correct grade in it. It's also worth taking off the rocker covers briefly with the engine running to check that there's plenty of oil getting up there - this will give you a good idea of whether there's a healthy oil flow around the engine generally.
Is the exhaust header pipe blowing? Is it correctly seated into the cylinder head with a proper exhaust gasket? If this was leaking near the head then it might cause slightly hotter running, and would sound very "clacky" near the cylinder head.
The ignition timing isn't adjustable - it's fixed by the position of the two ignition pulse coils. If one of these isn't working however, then the ignition won't advance correctly as the engine revs increase. This could also cause hot running, but would be accompanied by poor performance. To check this, go borrow a timing strobe and get someone to show you how to use it.
If there's plenty of oil flow and the exhaust header's OK, and the ignition is advancing correctly, then it might be fuel starvation causing lean running. You'd need to check the tank, fuel filter (in the tank), fuel lines, carb float bowl, float valve and jets for debris and clogging, and correct set up.
Does it have any other symptoms? What makes you think it's getting too hot? How long does it take to get hot, and doing what kind of riding? What kind of noise does the valve gear make and when does it start making it?
arrrf.
