Farmall Cub

Hi. I read some neat posts on how people test to see if their Cub is running rich and their applicable symptoms. I gave my manifold the finger-over-the-hole test. As I slowly moved my finger to allow a little air through I noticed the black liquid droplets and smoke spewing from my exhaust stopping within seconds. Seems to me Betty is drinkin' a little too much of the power juice. I checked my float and I'm at just about 1.15" from the gasket to the bottom of the float while in the closed position.

Two questions:

1) How can I tell what size main jet I have?
2) Who supplies replacement jets? I checked the sponsor sites and couldn't locate them. Unless I had one of those airhead moments and just didn't look in the right place. Hey it happens.

Zenith carbs are fairly common. Check the parts manual and a dealer should be able to get one.

http://www.thecarburetorshop.com/

Parts manuals provides an IH part number. Wisconsin engines commonly had Zenith carburetors.

Check for a number on the flat side of the main jet.

Guessing on my part, the main jet is not the problem.

Is there another part within the carb that would reduce the amount of fuel that is passing to the engine?

Calvin:

I would imagine that the Zenith has the same problems as the Donaldson carb when it comes to fuel starvation. I would check the cage for a flake of varnish or some dirt/crud. You may also want to check the neoprene coated needle.

Connecticut Calvin wrote:Is there another part within the carb that would reduce the amount of fuel that is passing to the engine?

The Zeniths run a little rich on cubs most of the time more so if it is a replacement carb [ one with 5 screws holding the half's together] Unless it is flooding I would not be too concerned
Boss

Connecticut Calvin wrote:Is there another part within the carb that would reduce the amount of fuel that is passing to the engine?

Higher then specified fuel level in the bowl.

Boss Hog wrote: The Zeniths run a little rich on cubs. Unless it is flooding I would not be too concerned
Boss

NAPA or Federated part number 7-02031. Part number in catalog says Wisconsin, on line says Clinton.

You will need to do some more research, but appears to be a Zenith carb kit and containing the main jet.

Lowered the float a hair, adjusted the carb air needle by loosening it one half turn then gave the timing a tweak by turning the housing and listening to the exhaust. I turned the housing counter clockwise until the engine begin to nearly choke itself out from firing too early then brought it back clockwise until it began to smooth out. I gave the tractor a test by trying to push some mulch with the front blade. Poor power. Cut out immediately. I did the same thing two more times moving the housing just about 1mm clockwise each time. Bingo! Super power! Low smoke! No more liquid spitting from the exhaust! It seems my fuel and ignition system adjustments were off just that much and they needed some help. Thanks for all the input gentlemen!

I been wondering if a adjusting main jet assembly can be used from another zenith carb with a larger jet that can be leaned a tad when adjusted. I think McDonald ignition could have the answer. I know I have also seen larger and smaller venturi for the zenith carbs too. We can adjust the cc' s of the air flow in the zenith carbs. Oops that's more info than I wanted to give away. Kidding. I'm thinking about building a super cub engine.

BigBill wrote:I been wondering if a adjusting main jet assembly can be used from another zenith carb with a larger jet that can be leaned a tad when adjusted.

Answer, probably and yes if the carburetor bodies are the same.

Zenith made several standard carburetor bodies, then changed the venturi and jets to match the manufacturer's engine application.