Zenith Model 20 and 23 carburetors were a 1-barrel downdraft carburetor used in the 1930s and early 1940s, notably on IHC 6-cylinder engines.
The Model 20/23 is similar to the 28/228 series, and uses the same float, but kits are different. Many have been replaced with Model 28/228 carburetors, and a new replacement carburetor, part number Y200 is available.
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How to find Zenith carburetor numbers