ohajoh

I have a Yamaha bayou 300, I think 1986, ran great till last year when it started to backfire a little. This year had trouble starting it up, changed the plug, and ran some carb cleaner through bust still sputtering? I adjusted the choke as it always had a problem staying running when the chock was open and now seems to be ok, but still sounds like it wants to backfire? Any suggestions???