 This washer limits how close the belt sheaves can come together, thus limiting the potential front diameter of the belt at full throttle.Removal of the washer is possible with simple tools and will increase the top speed to an RPM limited of 40 mph, although damage caused by modification is excluded from the Yamaha warranty.In Europe the Giggle Primary sheave variator (Part No 15PE76200000 ) is different from its US C3 version (Part No 3XYE7620010).