Well apparently according too the blurb on ebay it does all this "R&D Racing's new Power Pump w/adjustable leak jet (ALJ),
will allow you to tune your accelorator pumpsetting in seconds, for that crisp spot on throttle response
you are looking for.
R&D's ''ANTI-CAVITATION'' Accelerator pump chamber, is State of the Art, designed
with two separate fuel ports. Port one, is positioned at the highest point in the fuel chamber, providing a
natural purge, allowing entrapped air to escape through the leak jet orifice. Port two, is isolated low in the
fuel sump area, assuring 'FUEL ONLY' into the venturi. so i reckon it allows you too vary the amount of fuel used in the accelerator pump..........colin