Zenith Carb Intermittantly Running Lean

[tucker86]

As I have been running my 184 this fall, I have noticed three or four times now where I need to run with the carburetor partially choked. What is interesting is one week it runs perfectly fine and the next I will notice this issue. Outside temperature does not seem to a contributor to this condition as it has occurred when the temperature is up around 70F and also when around 40F. I tried playing around with the adjustment screw on the back side of the carburetor, but it did not make any difference with this issue and I set it back to the original settings. Since I have been running Seafoam through the fuel system, I was wondering if this might be caused by dirt in the carburetor? Thoughts?

[Bob McCarty]

I'd check to make sure the sediment bowl screen, the carb inlet screen, and the main jet were all clean and free of debris.

[Larry B]

If your carb is like mine the high speed jet is fixed. It is on the side near the bottom. A 1/2" wrench fits it. If you take it out and clean it fuel should flow out of the carb in a steady stream. If a fuel filter has been installed try removing it and see if that fixes it.

[Glen]

Hi,
Below is some info for cleaning the main jet on a Zenith carb.

Clean the outside of the carb well before taking it apart, if it is dirty, that keeps some of the dirt out of it.

The main jet is number 20 in the parts pic, it screws out of the carb. You need a screwdriver that fits it well, they have said on here to grind one to fit, if you don't have one.
The main jet is under the plug, number 18 in the pic.

http://www.farmallcub.info/manuals/cub_ ... 012-14.jpg

http://www.farmallcub.info/manuals/cub_ ... 012-15.jpg

The manual pages are from the Cub parts manual, I think the carb is basically the same.

Wash out the main jet, and where it goes in the carb, a member on here has said they often are dirty there.

There is a screen in the original fitting at the gas inlet on the Cub, if the 184 has the style fitting in the pic below, it may have a screen too. The screen has to be clean so the gas will flow.

I don't see a 184 parts manual in Rudi's manuals at the top of the page.

Below is a pic from TM Tractor of a Zenith carb for a Cub, showing where the cover is.

If any of this info look wrong, write a post saying.

[outdoors4evr]

Since it seems intermittent, I'd be checking the fuel tank vent (gas cap). Next time it happens, see if the issue is resolved by opening and re-sealing the gas cap. You may have a vacuum forming in the gas tank due to a plugged vent.

[tucker86]

Glen, great information. I'll look into your suggestions when I get some free time.

Since it seems intermittent, I'd be checking the fuel tank vent (gas cap). Next time it happens, see if the issue is resolved by opening and re-sealing the gas cap. You may have a vacuum forming in the gas tank due to a plugged vent.

outdoors4ever, I have inadvertently tried your suggestion. When this originally started happening I was thinking that I may have been running out of fuel and opened the gas cap to check. This seemed to have no effect, so it seems that is more likely an issue with dirt.

[Don McCombs]

Follow Bob’s suggestions.

[BigBill]

When I first got my 1st 154 home while mowing it would stall then a few minutes later fire up and finish mowing. As I continued to run it. It got worse finally it wouldn’t restart, I took the fuel line off no gas was flowing. I took off the gas cap and blew as hard as I could in the hose with the valve open. I heard a loud pop in the gas tank and fuel started flowing.

There was squirrel nuts in my gas tank, acorns.

On a dirtbike it would bog under a load. I found a little pebble in the main jet blocking the flow.

Pull the jet plug and look for a “alien” object. Check above the needle and seat for a pebble too. Installing a fuel filter in the line solves dirt problems.

[tucker86]

I cleaned the sediment bowl yesterday and did find a fair bit of debris in the bottom. The sediment bowl screen looked good.

One thing I did notice was when I opened up the sediment bowl valve after re-installation, the bowl refilled slowly even with the valve wide open. It took several turns before any fuel at all began flowing. It was getting late at this point and I wanted to park the tractor for the winter so I did not investigate further, but I am thinking there might be some debris slowing flow through the sediment bulb valve. I am thinking in the spring I will pull the tank and disassemble that valve as well as install an inline fuel filter. I could use the tank out anyway to look into the wiring at the switch for the lights.

[Jim Becker]

. . . I am thinking there might be some debris slowing flow through the sediment bulb valve. . . .

You may very well be onto something there. Sometimes trash can move around and only cause a problem part of the time, which could explain the intermittent nature of your problem.

However, I have also seen sediment bowls that were slow to fill because of an air lock. Temporarily loosening the nut that holds the bowl and allowing air to escape at the bowl gasket lets them fill quickly.

[A/C guy]

I had trouble with mine (don't think it is the Zenith). Opened it up and found the high speed metering jet had backed out a turn or so. Used a drop of blue locktite and reseated it. It's been good ever since.

[tucker86]

I'm working on getting the 184 ready for the mowing season and I rebuilt the carburetor today. I did not notice anything visibly wrong with it during disassembly other than the fuel pickup tube had a small amount of crystallization on it. After I got it back together I noticed the air intake end appears to not be sealing with the new gasket. I can see light passing between the fuel bowl and throttle halves on this end. I believe I read somewhere that Zenith added an a 5th screw for this issue on newer Series 68 carburetors.

I was wondering if others have noticed this and what has been done to seal this air leak? Silicone sealant?

[SamsFarm]

I'm working on getting the 184 ready for the mowing season and I rebuilt the carburetor today. I did not notice anything visibly wrong with it during disassembly other than the fuel pickup tube had a small amount of crystallization on it. After I got it back together I noticed the air intake end appears to not be sealing with the new gasket. I can see light passing between the fuel bowl and throttle halves on this end.

Sounds like something is hitting preventing the halves to close completely!

Did you change anything that might be a different length or thickness?

[tucker86]

I'm working on getting the 184 ready for the mowing season and I rebuilt the carburetor today. I did not notice anything visibly wrong with it during disassembly other than the fuel pickup tube had a small amount of crystallization on it. After I got it back together I noticed the air intake end appears to not be sealing with the new gasket. I can see light passing between the fuel bowl and throttle halves on this end.

Sounds like something is hitting preventing the halves to close completely!

Did you change anything that might be a different length or thickness?

I have been busy this past week and I am just getting back to this now. Below is a picture of what I am seeing. The seal around the fuel bowl area looks good and tight, but not on the air intake end. I was considering trying some silicone sealant on this end, but I wanted to see if anybody on the forum has seen this before. I wouldn't be surprised if the heavy layer of grease I cleaned from it was helping seal this end before the rebuild.

[SamsFarm]

Looks like it might be warped.

Take it apart and check it with a good straight edge.

Something like a 12 inch steel scale!