WOW, sounds like you have a GREAT mechanic. basically he is saying, "somethings wrong, i don't wanna fix it, lets throw expensive parts at it." fuck that guy, buy a clymer manual ($35) and a good set of tools (about $100) and work on it yourself. you will save a SHIT TON of money in the long run.
as for your problem, install the tors removal kit, then make sure all the moving parts in the carbs are clean, as well clean out and lube the throttle cable, and take the thumb throttle all the way apart and clean it out. the only way the bike can rev up is if the carbs aren't closing. the things i just told you to do SHOULD fix your problem...