2005 Polaris Sportsman 400/500 Service Manual, Page 121Get this manual
FUEL SYSTEMCARBURETION
VENT SYSTEMSCV CARBURETOR
The carburetor float bowl vent lines supply atmospheric pressure to the float bowlThe lines must be free of kinks, restrictions and be properly routedThis allows fuel to flow in the proper amount and prevents contaminants from entering the carburetor
CARBURETOR OPERATION CONT'D When the throttle plate is opened and engine speed begins to increase, the pressure in the venturi (and therefore in the chamber above the diaphragm) becomes significantly lower than atmosphericAtmospheric pressure in the chamber below the diaphragm forces the diaphragm upward, raising the slide against spring pressureWhen the pressure above and below the diaphragm are nearly equal, the slide moves downward under spring pressureRaising or lowering the slide increases or decreases the cross sectional area in the venturi, and therefore the air velocity in the venturi is kept relatively constantThis provides improved fuel atomization and optimum fuelair ratioLow Pressure From Venturi Vacuum Slide