24:1 is a safe fuel/oil ratio, I use 32:1 with no ill effects. (less oil spooge out the exhaust too)
If your engine is overheating, it is probably because of an overly lean mixture. If you do a lot of riding at WOT and high RPM's, the mixture could be leaning out. My bike has a pronounced "lean bog" when it approaches top speed, where the engine runs stronger at 3/4 throttle than it does at full throttle. I noticed this as the weather got colder (40's). It ran fine when the temps were in the 80's - but since cool air is more dense, more fuel is needed to keep the proper A/F ratio. The mixture seems rich enough at lower speeds, so for now, I keep my speeds around 20. The "proper" way would be to re-jet the carburetor with a larger main jet. The stock carbs have a mixture needle that you can raise or lower, and this will adjust idle/mid range mixture - but maximum flow is regulated by the main jet.
During normal operation, the cooling head and fins on the barrel are too hot to touch. An overheating engine should burn flesh almost instantly.