Ron at RB-Designs has a carb mod and a carb fix. The fix is to replace the worn nozzle. This is the orifice that the needle fits into.
Ron guesses that the excessive wear that some bikes see in this area is due to the use of the boyeson rad valve and it's associated short carb insulator (the rubber piece is short and doesn't isolate the vibrations from the reed valve and motor from the carb itself).
If your bike has a bit of time on it - a worn nozzle might be contributing to your problems. If you send your carb to Ron you can have him replace the nozzle along with his other mods... (by the way, he is the only one who can replace the nozzle for you as Keihin doesn't sell this as a replacement part - he makes them up himself).
jeff
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