I believe the knurled screw you are referring to is a part first seen on the K1. I imagine Honda came out with this feature because of complaints about the stiff throttle pull while holding the twist grip in a sustained open position. This setup acts as sort of a "cruise control," keeping the throttle from snapping shut while open, but does nothing to lessen the throttle pull. This setup can be used on earlier CB750's, by loosening the nut and removing the slotted screw, which in effect, does the same thing as the knurled screw, only less user friendly when under operation. Using this setup, I seem to recall there is a different (longer) tensioner spring used inside the throttle housing.