Sounds like some dirty air bleeds.  On the top cover of the Teapot carbs, there are some very small air bleed holes that can get dirty.  Shoot some carb cleaner through those holes.  Also check that the machine screws holding the carburetor top cover in place are ‘snug’ as well as the center bolt that holds the air cleaner stud.  A worst case scenario is the top cover gasket no longer sealing the cover properly to the carb fuel bowl.

I’ll add that performing a ‘running flush’ on the carbs might also fix the problem. Here’s the link to the past thread explaining in more detail what a ‘running flush’ is.