So i bought a predator 212cc and had the intention of putting it on a go kart frame, i did it and it worked for a while. the engine when i took it off choke and feathered the throttle it would start to rev up buy itself and made an unusual high pitched noise. not like scraping like a two stroke at high rpms. i didnt know what to do so i took it back to the store and traded it for another one and it now does the same thing. auto teacher said its probably running lean. Im stuck havent done anything to it besides put oil and gas in it. thanks for any help.