i just bought a 2006 gs500f with 9500  miles and i think it may have been sitting around awhile.  I took choke mechanism apart and found cob webs.  i replaced front and rear brake pads, replaced air filter, removed fuel tank, replaced fuel lines from tank to fuel chicken.  ran good for about 200 miles then started over revving all by itself.  Starts good and idles when cold but when operating temp is reached the engine revs to almost 4000rpm and will not return to idle.  I can force idle by using first gear and clutching it down. 
Any suggestions or ideas? 

Ray

hmm i had the same thing happen to my 93 gs500e but it could be a stuck float in a carb, or they need to be cleaned if its been sitting for a while. also make sure the choke isnt stuck on.(check the carbs choke rod that its not stuck)

Idle screw?  What happens if you turn that way out?

It shouldn't idle nice when cold, it should be miserable without the choke.
Once got mine back from the dealer idling nice with a cold engine. Yeah, by the time I got home, idle was ~3k. Called 'em, asked if they adjusted the idle, 'nope' was my first answer. 'Maybe backed it off a little' was the second. Yeah, my a**.

tl;dr: adjust the idle screw after a good long ride, keep it alive with the choke when cold.

+1 on the idle screw. If you set the idle before the engine is totally warmed up, you get the symptoms you are describing.

Thanks for all the suggestions, I will check each one of them out and let u know what is happening....