Horstman DXL-991 is a 4 spring wet clutch designed solely for two cycle kart racing.Special oil is added through the oil cover to dissipate heat as well as raise the stall speed to the necessary level for best performance. The DXL-991 fits the popular Yamaha KT-100S kart engine. New feature for 2010 is an aluminum drum for faster heat transfer. A bolt-on sprocket reduces cost when replacement is necessary.