2001 Polaris SLH, Virage PWC Factory Service Manual, Page 116Get this manual
CarburetionExhaust 2001 Keihin 40mm LE Carburetor System Overview
The Keihin LE carburetor is floatless diaphragm type Several separate but overlapping systems are used to meter fuel and air properlyAir Metering System
The metering of air is controlled by the throttle plate The position of the throttle plate determines which fuel delivery system or systems supply fuel from the fuel chamber to the engineInlet Need le Valve Syst emFuel Chamber
The amount of fuel allowed into the fuel chamber is controlled by the inlet needle valve assemblyOpening and closing of the valve is controlled by regulator diaphragm movement and spring pressure under the control armThe regulator diaphragm is sealed to the carburetor body forming two chambersOne side is vented to atmospheric pressure, the other side (fuel chamber) is exposed to the venturi (low pressure) through the fuel delivery jets and passages Atmospheric pressure pushes on one side of the diaphragm, applying pressure on the control arm in the fuel chamberThis reduces pressure on the inlet needle and allows it to lift more easily off the seatWhen the engine is running, pressure in the carburetor venturi (and therefore the fuel chamber) is less than atmosphericThis increases the effect of the atmospheric pressure on the diaphragm and lever and overcomes spring pressure When the lever return spring pressure is overcome by these forces, the needle lifts off of the seat or "pops off", allowing pressurized fuel from the fuel pump to enter the fuel chamberFuel inlet needle "pop off" pressure is influenced by many factorsAtmospheric pressure, venturi low pressure, the amount of spring pressure on the control armand fuel pressure from the fuel pump all have an affect on operating pop off pressureAll of these forces combined regulate the amount of fuel that enters the carburetor fuel chamber and the engineChanges to pop-off pressure are not recommended