2009 Polaris Scrambler 500 4x4 2x4 factory service manual, Page 135Get this manual
CLUTCHING DRIVEN CLUTCH OPERATION CONT'D
As engine RPM and horsepower increase, the load from the drive belt increases, resulting in the belt rotating up toward the outer diameter of the drive clutch sheaves and downward into the sheaves of the driven clutchThis action, which increases the driven clutch speed, is called upshiftingShould the throttle setting remain the same and the vehicle is subjected to heavier load, the drive belt rotates back up toward the outer diameter of the driven clutch and downward into the sheaves of the drive clutchThis action, which decreases the driven clutch speed, is called backshiftingIn situations where loads vary (such as uphill and downhill) and throttle settings are constant, the drive and driven clutches are continually shifting to maintain optimum engine RPMAt full throttle perfectly matched PVT system should hold engine RPM at the peak of the power curveThis RPM should be maintained during clutch upshift and backshiftIn this respect, the PVT system is similar to power governorRather than vary throttle position, as conventional governor does, the PVT system changes engine load requirements by either upshifting or backshiftingair ducts, as well as the inner and outer covers, must be properly sealed to ensure clean air is being used for cooling the PVT systemThis also will prevent water and other contaminants from entering the PVT areaA sealed PVT is especially critical on units subjected to frequent water forging