The Mikuni BS CV carbs have a pilot screw which control how much fuel/air emulsion enters the airstream, which affects mixture at low throttle openings and idle. More open = richer. Typically the flow maxes out at about 3.5 or 4 turns open. If you don't get the results you need then it's time to step up the pilot jets. I would not up size the pilot jets as a matter of course though. It's not needed on an otherwise stock bike.
