1949 Cub Carburetor

[Slim140]

Thanks for the feedback. Update for everybody that is wondering, I purchased the tractor yesterday and it went very well. We loaded up the tractor and brought it to my house. I drained all the gas that has been sitting in the tank. And put fresh 87 octane into the tank. Surprisingly, the tank is not rusting at all. It has been converted to a 12 V system, so I grabbed a standard 12 V battery and hooked it up. After a few cranks it started right up, but was smoking a lot. Now I know what he meant by a carburetor issue. It only runs with the choke on and bogs down when I try and put it into second.

Sounds like it may be time for a compression test, the carb may not be your problem.

[Flowmaster76]

It only smoked when I first started it. I think that was because it was sitting for a while. After about a minute the smoked stopped. But it wouldn’t hurt to do a compression test

[tmays]

I’m thinking it is not getting enough gas, so I will be thoroughly cleaning out the carburetor today.That will eliminate the issue of things inside the carburetor. One of my original concern is that the previous owner does not have the original fuel set up. The fuel sediment bowl has been completely removed. The only filter is an in-line fuel filter.

Inline filter is fine as long as it’s a gravity flow filter. Of course you can’t tell by looking at it. Probably have to check the flow by taking out carb main jet or some other point. Or just replace with sediment bowl or replace filter with known gravity flow one

[Don McCombs]

Did you get oil pressure when you started it?

[Glen]

Hi,
If the fuel system has an inline filter, they have said on here before that it has to be a filter for a gravity feed fuel system.
There are inline gas filters for use with a system with a fuel pump. They have said on here before that they may not work right using them on a gravity feed system. Not enough gas flows through them.

You can do a gas flow test, disconnect the gas line, below the filter, and hold the hose over a clean large can, and see how fast the gas runs through the filter. If it is slow or stops some, it needs improving. Let it run for 1 minute. You can reuse the gas, if you catch it in a clean can.

The gas tank cap should be vented, and have vent holes. The holes have to be kept open. Use a small wire and clean the holes if they are plugged. Plugged vent holes will stop the gas flow.
You can remove the cap for the flow test also.
If you can't get enough gas flow, try buying a gas filter for a gravity flow system, and put it on, and try the flow test again. Stores that sell parts for small engines probably have them.

It looks like in your pic that the Cub has a Zenith carburetor, which was used on Cub engines beginning in 1975.
A closer pic of it would be good.
There is a main jet on them that can be plugged, then it won't run right.
If you don't find anything wrong following what I wrote above, you could clean the main jet. It is under the hex headed cap at the bottom rear of the carb.
Use carburetor cleaner, and then blow it out with compressed air. Use your safety glasses when using the air.
I don't think the jet needs removing to clean it. If you remove it, use a screwdriver that fits well, they have said on here before to grind a screwdriver to fit it, if needed, and don't slip it in the slot.

Below are pages from the Cub parts manual, showing the Zenith carb.

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

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

Below is a pic from TM Tractor of where the main jet is on a Zenith carb.

[Flowmaster76]

Here is a picture of the carburetor. I bought some carb cleaner that you place the carb in a strainer submerged in the cleaner and let it set. I’m going to do that right now. When I first started it, it had good oil pressure. It stayed constant the entire time it was running.

[Flowmaster76]

I have started to take it apart

[Flowmaster76]

Here is me starting to take it apart. I put it in the carb cleaner and am going to let it sit overnight.

[tmays]

Isn’t that the wrong Zenith carb for a cub? Possible the main jet orifice is too large?
Been a few years since I’ve handled one, so I could be wrong

[Flowmaster76]

Oh really?? It might be the main jet then.... hmmmm. I haven’t taken the main jet out yet but on the top of it it said 25. Not sure if that means anything.

[Bob McCarty]

Don, Bill, and I took apart a Zenith at Cecil's. The main jet should be a 21, bleed a 34, idle jet a 12, discharge nozzle a 50, venturi 15 mm, and the needle valve seat a 35. That's from the Blue Ribbon Service Manual GSS-1411. Bill was able to get the correct parts from McDonald Carb. The #'s are part #'s and not drill sizes like on the IH carb.

[Bill Hudson]

… The main jet should be a 21... Bill was able to get the correct parts from McDonald Carb. The #'s are part #'s and not drill sizes like on the IH carb.

The main jet I got from McDonald carb is a 19. I got it after talking with the fellow at McDonald. Got the parts today and put them in the carb. Placed it on my test mule and it ran like a top with none of the problem associated with the main jet that was in the carb.

Bill

[Eugene]

Sounds like it may be time for a compression test, the carb may not be your problem.

Yup. My vote is for a 100% engine tune up which includes compression tests.

Actually that carburetor appears to be very clean. I would have just use the spray carburetor cleaner. To me the carburetor appears to have been recently installed on the tractor - not dirty enough on the outside or inside to have been used very much

If you are still in contact with the seller, ask if he still has the old junk carburetor.

[Glen]

Hi,
They have said on here that there is originally a screen in the 90 degree fitting at the gas inlet to the carburetor.
It should be checked to be sure it is clean.