The Zenith model 29 and 129 were large single barrel downdraft carburetors with a double venturi, twin floats and concentric float bowl. The concentric design, where the fuel surrounds the float and the discharge jet (nozzle) is centered in the float bowl, allowed for operation at extreme angles without flooding the engine. Model 29 carbs were built in Zenith size 11 (SAE 1-3/8" nominal throttle bore) to Zenith size 16 (SAE 2" nominal). Model 129 was size 16 only.
This series of carburetors was used on trucks, machinery and military venicles from 1941 into the 1960s. Notable examples include fire trucks, including American LaFrance, and military vehicles such as Brockway B666 and C666 6X6, 6 ton trucks, White M3 Scout Car and others.
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How to find Zenith carburetor numbers