Cub carb replacement

[nc460]

This is my first post but I got my grandpa's old cub and it has developed a gas leak from the carb. It was rebuilt a while back and I was wondering if I would be better off rebuilding it or getting a new carb.

[Don McCombs]

When and where is it leaking? While sitting? During an attempted start? While running? I would clean the carb and adjust the float before I contemplated replacing the carb.

[Glen]

Hi,
Welcome to the website.

The needle and seat might have dirt in them, and not seal, causing the dripping. You have to take the top off of the carburetor to clean the needle and seat.
The carb can drip from the float level being too high also.

It is normal for a Cub to drip gas on the ground, if you were trying to start it, turning the engine over, and it won't run. The updraft carb lets the gas out the drip hole on the bottom that was going up to the cylinders because of the engine vacuum. The gas runs back down, and drips out.

If you were not turning the engine, then it should not drip.

Here is info for setting the float height, and float drop, for the IH carburetor, and removing the top half of the carb.

The IH carburetor is easy to work on.
The top half has to be taken off the carb to set the float level.
When taking the top half off the carb, pull it straight off the bottom half 3 or 4 inches, there is a small idle tube that is screwed into the top half, that sticks down into the bottom half. If you twist the halves, or strain the tube too much, it can break off. Then you have to buy a new tube and repair that.

Clean the carb with solvent, or carb cleaner, and blow out all passages with air. Wear your safety glasses when using the air.

Below is a page from the Cub service manual, showing the float level, and float drop for the IH carburetor, in the upper pics. It should be set to exactly the specs shown.
The top half has to be removed from the carb, and turned upside down, like the pic of the Zenith carb, on the lower right of the page.
Bend the float arm, between the float and the pivot to change the float height, but not right where the end of the needle touches it.
Be sure to use the specs for the IH carb.

Turn the top half right side up to set the float drop.
The tab on the float is for the float drop, it stops the float from dropping too far. Bend the tab to change the float drop.
You need a measure with 32nds of an inch markings.

http://www.farmallcub.info/manuals/gss- ... 002-09.jpg

The IH carb float level is measured without the gasket between the halves in place.
People have posted on here that their carbs would not work right, until they set the float level exactly.
Tighten the screws and everything on the carb gently, the metal is soft, and the threads can strip.

The needle and seat wear after years of use, then they don't seal, that can cause it to drip on the ground when sitting. Then the needle and seat need replacing.

Below is a listing for a new needle and seat at TM Tractor. They have other carb parts also. They are at the bottom of the page.

http://www.tmtractor.com/new/fl/5183fp.htm

Below are pages from the Cub parts manual showing the IH carb.

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

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

[nc460]

So it leaks when sitting. As far as I can tell it looks to be coming out of the throttle shaft where the linkage to the hand control is. Also it looks like the pressed in plug on the bottom of the carb under the throttle shaft is oozing. I sat there with a rag and brake clean trying to clean and watch where the gas came from.

On another note, where the hand throttle linkage meets the throttle shaft supposed to be spline? Mine seems to be loose or slipping on the shaft. Not sure if that's normal

[Glen]

Hi,
Below is a pic from TM Tractor of the engine side of the IH carburetor.
The throttle rod connects to the linkage at the top of the carb. The linkage piece is riveted tight onto the throttle shaft.
The choke rod connects to the choke lever at the lower right in the pic. The choke levers sort of commonly come loose. The screw needs tightening to tighten it. There is a spline on the choke shaft for the soft metal of the choke lever. The lever usually needs to be in the position shown, when the choke is fully open.
The gas is supposed to drip out the drip hole at the bottom of the carb, if there is a leak from the needle and seat, or if you were trying to start the engine, and it didn't run, like I wrote above.

[nc460]

Thanks. And in the post above I misspoke I meant to say choke rod. I had my orientation backwards. So rebuild time

[yellowcub]

I set my float height with the gasket in place. I have a NOS Carb and the gasket is paper thin. Todays IH gaskets that I use are thicker. If the height is that important, then the gasket thickness matters. Also, leaking may be caused by the needle valve body and the top half of the carb. That washer sometimes can't make up for the pits, so use gas thread sealant on the threads. Someone on this site suggested to use a lighter needle so when I rebuilt my Briggs& Stratton generator carb, it came with 2 needles and the one that did not fit the generator carb works perfect in my IH Carb.