Switching back to the IH carb
Mike
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Zenith Carb ? ?
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Arizona Mike
- Cub Pro
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1947 Circle series Farmall Cub with Armstrong lift, belt pulley, 5"rims 6" tires, SN 563
1949 Farmall Cub with high crop option and hydraulics
1955 Farmall Cub with fast hitch
1955 International Cub Loboy with fast hitch
1957 Farmall Cub with fast hitch
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Lurker Carl
- Cub Pro
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Mike,
Since you're taking the Zenith off, here's some things to check for.
Be positive your Zenith carburetor is for a Cub - the Zenith aluminum model 68 carburetor was used for just about any engine from 25 to about 170 cid in automobiles, boats, tractors, etc. They all look about the same and most will readily interchange. The Cub Zenith has a 15mm venturi, #21 main jet, #12 idle jet and #50 main discharge nozzle (21, 12 and 50 are Zenith ID numbers, NOT drill sizes). Sometimes these numbers are stamped on each item, other times not.
Measure the fuel level. Using the same technique as the IH carb, fuel level in the bowl should be 15/32" below the machined edge of the bowl casting when mounted on the manifold. Also, make sure fuel isn't leaking past the gaskets for the float cage and main discharge nozzle, the float cage/needle assembly are a matched set, and the idle and main jets are not damaged. With the engine at operating temperature, fine tune both jets by setting idle speed first, then idle jet and main jet adjustment for smoothest operation.
Zeniths have a tendency to wear away the side of the throttle plate as the shaft bushings wear out. The gap will be obvious when you look at the throttle plate in the carburetor plenum. This will cause idle and low speed problems that disappear at higher RPMs.
Carl
Since you're taking the Zenith off, here's some things to check for.
Be positive your Zenith carburetor is for a Cub - the Zenith aluminum model 68 carburetor was used for just about any engine from 25 to about 170 cid in automobiles, boats, tractors, etc. They all look about the same and most will readily interchange. The Cub Zenith has a 15mm venturi, #21 main jet, #12 idle jet and #50 main discharge nozzle (21, 12 and 50 are Zenith ID numbers, NOT drill sizes). Sometimes these numbers are stamped on each item, other times not.
Measure the fuel level. Using the same technique as the IH carb, fuel level in the bowl should be 15/32" below the machined edge of the bowl casting when mounted on the manifold. Also, make sure fuel isn't leaking past the gaskets for the float cage and main discharge nozzle, the float cage/needle assembly are a matched set, and the idle and main jets are not damaged. With the engine at operating temperature, fine tune both jets by setting idle speed first, then idle jet and main jet adjustment for smoothest operation.
Zeniths have a tendency to wear away the side of the throttle plate as the shaft bushings wear out. The gap will be obvious when you look at the throttle plate in the carburetor plenum. This will cause idle and low speed problems that disappear at higher RPMs.
Carl
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