A can of seafoam or Gumout with Regane in a tank of gas might clear it up. There is a "shotgun method" of trying to clean up carbs without removing them and Cowpuc has a method where he uses a turkey baster to pump some carb cleaner into the carb bowl and pull it out and keep doing this a few times. I don't remember all the details. If you do a search of this site you might find the details of the shotgun method and Cowpuc's method. Also, cowpuc has youtube videos listed under puc puc. You might find his method there. If the bike has been sitting a while the carbs usually need some cleaning.