The Zenith model 29D (D = duplex) series carburetors were a large two barrel downdraft carburetor with a twin-pontoon float and a concentric float chamber. They used a power piston/accelerator pump combination that operated by vacuum, and some models used a governor between the carb and intake manifold. Both Pierce and Zenith Mechanovac governors were used.
The body consists of three major castings and is made of cast iron, with cast zinc venturi inserts. They were used on large trucks and industrial engines, including Continental, Federal, Hercules, Mack, Oshkosh and Waukesha. Many are found in American LaFrance, Seagrave and other fire trucks. The carbs were produced in Zenith size 13 (1-5/8" SAE nominal bore size) and size 14 (1-3/4" SAE). In practice, the 29D14 carburetor had 1-15/16" throttle bores. The mounting flange bolt centers were 3-5/16" wide by 2-13/16" deep.
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How to find Zenith carburetor numbers