Electric Choke Mechanical Secondaries-4150; Holley upgraded their two most popular sizes of double pumper with electric chokes. The 650 and 750 CFM models are available in the classic zinc and shiny polished finishes. Holley Double Pumper® carburetors are a perfect performance upgrade for hot street cars and race vehicles. Double Pumper carburetors are an American icon when it comes to performance carburetors. From their roots as the premier carburetor on many factory muscle cars to powering thousands of vehicles across the finish line, the Double Pumper is a great choice whether you are burning up the street or the quarter mile.