Willy's Carburetor metering block valves allow you to convert your carburetor equipped with Willy's externally adjustable metering blocks to a completely different jet sizing range. Each click will allow you to raise jetting by 2-4 sizes, depending on your application. They are manufactured from high-quality brass for superior strength and maximum durability. Willy's Carburetor & Dyno Shop metering block valves are available for both the primary and secondary float bowls and can be used on gasoline and alcohol fuel systems.