[Rick Parker]

It provides a 3rd hole from which fuel can be drawn from while still remaining on the idle circuit as the throttle plate is progresively opened. It keeps the idle circuit in use longer before transitioning to the Main circuit of which the emulsion tubes play a very significant part. One other critical item is the throttle shafts sometimes have to be slightly twisted to "adjust" the throttle plates orientation, so they are precisely syncronized in uncovering the idle progression holes at the exact same rate, if one plate is "Ahead" of the other, progression will not be as smooth.