The pump diaphragms in Keihin FCR carbs was originally designed to feed FOUR carburetors in a row on bigger displacement motorcycles. The single cylinder dirt bikes with FCR-MX carbs use a "LEAK JET" to reduce the total pump volume squirted, by sending the majority of the fuel back into the float bowl. This helps prevent flooding the motor in slower riding conditions where the throttle is being opened and closed repeatedly at low RPM.
---Either a short-stroke diaphragm, and/or a leak jet, will reduce the pump squirt volume.
Picture thanks to Lucky at forums.sohc4.net