buell s1 lightning '97 マニュアル

 

See 

 The accelerator pump system uses sudden

throttle openings (rapid acceleration) to quickly inject fuel into
the carburetor venturi; the extra fuel provides for smooth
acceleration. This fuel also assists engine operation during
cold engine warm-up when the enrichener is turned off pre-
maturely.

Rapid throttle action, during the first third of throttle travel,
causes the accelerator pump rod to depress the accelerator

pump diaphragm. This forces fuel in the pump to flow through
a fuel passage (which has a “one-way” check valve), through
the pump nozzle, and then into the venturi. When the throttle
closes, the pump rod lifts up and away from the pump
diaphragm; a spring below the diaphragm pushes the
diaphragm upward, thereby causing the lower pump cavity to
refill with fuel from the float bowl. The check valve prevents
backflow of fuel from the pump nozzle/fuel passage during
this refilling phase.