Farmall Cub

So I decided last fall to order a new carb for my Allis B. The one on it was physically damaged so I knew I needed to replace it. As it turns out the same carb for the Allis B also works for the 140. So I decided to just replace the 140 carb, and use the old one from the 140 on the Allis B. So the new carb comes in just fine but I noticed right away that the linkage for both the choke and the throttle are upside down. Course that is where they are supposed to be for the Allis so it made sense. They are adjustable and the book says to just use the old carb as a reference. That turned out to be an issue. I thought I got things as best I could but the first issue is that the tractor will not idle. I can get it to idle at 550 but the speed control lever is off it's last teeth. If it is on the last tooth it will idle at a bit above 1000 any adjustment and the governor moves it right back to 1000. I do have it adjusted at 1550, but it does not seem to want to pour on any juice when you come under a heaver load. Tonight mowing going up my hill from my pond it seemed to struggle. I never had this issue before I swapped carbs. My guess is that I don't have the throttle lever on the carb set correctly. My plan at this point is to pull it back off and set it again. Does anyone have a good idea about how to go about doing that?

Thanks!

Well I called Zenith Fuel Systems yesterday and they really had no advice on how to set the throttle linkage. So, since I am off the rest of this week I am going to work with the old carb again and see if there is a way to measure the angle. Maybe if I lay the carb flat on the workbench and try to measure the angle from there.

That's assuming the venturi and jetting are the same for both tractors...

I had a Zenith carb for my LoBoy, which had the wrong venturi. It never ran quite right.

Matt Kirsch wrote:That's assuming the venturi and jetting are the same for both tractors...

I had a Zenith carb for my LoBoy, which had the wrong venturi. It never ran quite right.

Well now that is something that I did not consider. I might just call them again and see what they say.

Since no one has replied to this post I may just put the old carb on and deal with the new one on the Allis. That is unless someone has some suggestions?

Have you thought about using the throttle shaft from the old carb. These should be set in the correct position already, then you can use the new ones on the allis. Just a thought!

raystractors wrote:Have you thought about using the throttle shaft from the old carb. These should be set in the correct position already, then you can use the new ones on the allis. Just a thought!

I'm going to look again, but I think the last time I looked there is some type of retainer on the end of the new carb's shaft. Didn't look like it was meant to be removed again. But, tomorrow I will have more time so I will look again then. This is a good suggestion though!

Heed Matt's comment on venturi size. Same thing with jets. Put the original carb back on the 140 the way it was. You should then have one tractor running right, maybe both.

I have a question what is the Venturi and how would I know if I purchased a new carburetor for a specific tractor giving the model # for this to be correct?

The venturi is an internal part to the carburetor. It is the part where the air and fuel are mixed together.

It's where the neck of the carburetor kind of pinches in and then widens back out, right near the fuel nozzle. The pinched in part causes the air to move faster and mix around.

On a Zenith, these are interchangeable. You can get different-sized venturis for different tractors.

When you buy a carb, you simply have to trust that what you are getting is the correct one for your tractor. There aren't many people, if any, who would know off the top of their head which part # venturi goes with which tractor.

In this case, he's trying to make a carb designed for the Allis work on a 140, and is having problems. The carburetors may LOOK the same on the outside, but they could be very different on the inside...

Matt,
Thanks for the info on the venturi! I had no idea this part on the carb made such a difference and infact just purchased a used carb for my Super A and will review the parts manual to verify this carb has the correct part.

Quick Update

I called Zenith fuel system and really the correct model replacement for the C123 engine is a model 12911 zenith, and not the 12522 that I was shipped. However the carb store shows both tractors using this same carb. I called Zenith fuel systems and got some basic information on both carbs and what the differences were. The venturi on the 12522 is 16 while on the 12911 is a 15, The main jet is fixed at 19 on 12911 and is adjustable on the 12522 from 0 to 26. the only other difference he noted was the Well Vent on the 12911 is an 18 while on the 12522 is a 15. I am not sure what differences these numbers will make so that is why I posted them here for opinion. The 12911 is still available and I did find one retail outfit for it. When you look at the pictures it looks exactly like the one taken off the tractor.