When replacing the RH brake switch I discovered a knurled (adjustment?) knob on the lower inward side of the throttle twistgrip. There is no reference to it in my Owner's Manual. Is it perhaps an idle adjustment? I've not been prepared to make an adjustment in case I stuff something up; the bike is running very well at the moment with 23736MILES on the odometer. Can anyone please tell me what the knurled knob is for?