Nice bike! Never had issues with my tranny doing that. The rev hang is an issue? There are some things that need to be checked first. I know I wont get all of them and the more brainy peeps will be along soon. Since you don't know the condition of the bike you need to see how mechanically sound it is. You could have leaking intake gaskets, which is a thing for these. Start with the basics on the tranny. Hows the fluid, clutch adjustment, cable?