These Keihin 28mm PWK carburetors are great for dune or trail motors in a wide variety of sizes. Great replacement for the stock carburetors will fit in stock intake boots and provide great fuel economy in compared to some other carburetors. These come with lighter springs for less thumb fatigue. Keihin PWK carburetors is the dominant carb on the factory machines. In short because of their great performance they come stock on a lot of the leading brand bikes. Above All PWK Features are. Chromed semi-flat (D) throttle valve for excellent response and more flow at high RPM. Throttle bores sized to give maximum power. Easy jetting with jetting parts available. Quad Vents: Eliminates post jump bogging from fuel plugged vent passages.