2003 Polaris Freedom, Virage and Genesis PWC Service Manual, Page 154Get this manual
FuelExhaust Fuel Pump Operation
When the piston is on the upstroke crankcase pressure is low, the diaphragm in the fuel chamber moves outward toward the chamber coverThis causes negative (low) pressure in the fuel chamberThe check valve on the fuel supply side of the chamber opens, allowing fuel to enterThis vacuum causes the outlet check valve to close so fuel cannot return from the carburetorSee Ill1Ill1 Piston on upstroke Inlet check valve open Outlet check valve closed
Negative (low) crankcase pressure