The tractor is runing too rich.

[Baxter28]

I just rebuilt the carb on my 1952 Cub and it is still running too rich. Here are a few questions so I have a game plan before I remove the carb again.

a) Should the choke shaft lever be flat against the friction spring?

b) I double checked the float level and drop when I rebuilt the carb. If I need to make modifications to either, how much and in what direction to run a little leaner?

c) Is there any good or easy method to check the hole size in the main metering jet?

Thank you all in advance.

[Bob McCarty]

A) If this is an F Cub, the choke lever should be on the opposite side of the spring. Spring away from the engine, choke lever on the carb side nearest the engine.
B) I'm not sure how much help adjusting the float will make, but you'd want to decrease the drop to close the needle valve sooner (I think)).
C) You'd need to have either a set of wire gauges or set of numbered drill bits. If you can read the part # on the flat top of the carb adjacent to the gas inlet, we can tell you what the jet size should be.
If your plugs are fouling you may need to run a hotter plug.

Bob

[Glen]

Hi,
Here is a pic of a Cub carburetor installed, from TM Tractor. The choke is in the fully open position in the pic. The spring should rub on the lever in any position, and make some friction.
Lowering the float level slightly makes the carb work more lean, but not sure if you should do that. The experts will probably say what to do.
Here is a page from the Cub service manual showing the carb specs.

http://www.farmallcub.info/manuals/gss- ... 002-02.jpg

[Baxter28]

Thanks for the photo. I can see that my choke not quite open the whole way. Looks like I have the first issue to fix.

[clm2112]

Just a thought,

If the carb is running the engine rich all the time, I would be looking for a problem with the air bleed passages and gasket. This carb style uses bleed air to lean the mixture based on airflow through the carb. Any obstructions in the air bleed passages or air leaks in the gasket would push the mixture towards the rich side all the time.

[Glen]

Hi,
Here is a pic of the carb from behind it. If your choke rod is the original length, the choke lever should point about straight down. It is adjustable on the shaft, loosen the little screw, and it turns. Tighten the screw firmly when it is adjusted right, the screw comes loose sometimes over the years.
The 2nd pic shows the choke rod at the Touch Control tubes, it should be above the tubes some, when the choke is open. Sometimes the rod is too low, and rubs on the tubes, that can cause vibration wear if you are using the Cub for work.
If it is rubbing, increase the bend, seen in the pic, that should raise up the rod from the tubes.

[Baxter28]

I took a real good look at the IH parts breakdown in the service manual. I am almost positive that the part called the #17 Main Air Bleed is not in my carburetor. Was this item eliminated at some point or did a previous owner remove/lose it?

[Don McCombs]

It should be there. It is brass, so it should be easily seen.

[Matt Kirsch]

One question: What makes you think the tractor is running too rich?

[Baxter28]

All the normal indicators such as the plugs, the new rain cap is sooty black after about 1-2 hours of running, etc.

[Glen]

Hi,
Here are pages from the Cub parts book showing the IH carb. The part you said is number 30 in the pic.

http://www.farmallcub.info/manuals/cub_ ... 012-12.jpg

http://www.farmallcub.info/manuals/cub_ ... 012-13.jpg

[Baxter28]

I worked on the carb today. I re-checked the float level and drop and both were good. I also checked all the air bleed circuit with a small wire to verify they were all open. I then cleaned them with spray cleaner. I also adjusted the choke shaft and plate so the choke would open completely. This choke and idle air adjust went a long way towards making the engine run cleaner. I mowed a 1/2 acre of grass and liked the results.

[Glen]

Hi,
Glad it is working better. Not sure if anyone said above, the idle mixture screw on top of the carb needs adjusting, the owner's manual says start with 1 turn open, but it usually takes more open than that, maybe 1 1/2 turns, you just have to warm it up good and see. Some might not need that much open.
Here is the page, it is at the lower left.

http://farmallcub.com/rudi_cub/www.clea ... age-22.jpg