1999 Polaris SLH, SLTH, SLX, SLTX, PRO785 Factory Service Manual, Page 92Get this manual
FUEL SYSTEMCARBURETION System OperationMikuni Carburetor Carburetor System Operation Pop Off Pressure
Carburetor pop-off pressure is pre-set at the factory for given engineTest as outlined on following pageIf pop-off pressure is incorrect, follow the procedure below to find the causePop-off pressure should not be changed to correct running condition problem unless required by changes in elevation, or enginecarburetor modifications for racingFuel inlet needle "pop off' pressure is influenced by many factorsAtmospheric pressure, venturi vacuum (low pressure), the amount of spring pressure on the control arm, fuel pressure from the fuel pump, and the size of the needle and seat 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 engine
Needle ValveDiaphragm Operation
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 arm"'C 11 Ie D