Zenith K5, K6 and model 50 carburetors were cast iron updraft carburetors manufactured in the 1930s and 1940s. They were a 3 piece design where the choke plate was in separate section (the airhorn) at the bottom of the carburetor. The K6 was larger than the K5. Model 50AY12 was a Zenith size 12 (1-1/2" SAE nominal bore) carburetor made for IHC.
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How to find Zenith carburetor numbers