2003 Polaris ATV Trail Boss 330 Factory Service Manual, Page 98Get this manual
FUEL SYSTEMCARBURETION 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 ratio
Diaphragm Low Pressure From Venturi Vacuum Slide
From Air Box
STARTER SYSTEM (CHOKE OR ENRICHMENT)
When the choke cable (1) is activated, the starter plunger (5) is lifted off the seat8 5