These CNC-machined metering blocks are available for both the 4150- and 4500-style carburetors. Machined from a solid aircraft grade aluminum billet, they are immune from the porosity problems found in stock cast metering blocks. They provide stable, consistent fuel metering for all applications. Alcohol metering blocks are hard anodized. These are bare blocks, with no jets, power valves, air bleeds, etc.