Help with a Cub! Fuel issues????

[72chevelle]

Hello,

I have a 65 Cub hat I have been trying to get back into service. I went through and did new points, cap, rotor, wires, and plugs. Went through and soaked 2 gallons of evaporust in the tank for a day and drained it and rinsed it with water, then with gas. I rebuilt the carb which was updated to a zenith carb years ago. Now i have it where it will run perfect with the choke on but as soon as I let it off it dies. I initially though an air leak so I got a new intake/exhaust gasket and installed it and a new carb gasket and still the same thing. When I spray starting fluid around it while its running (with the choke on) it doesn't rev up at all. Could my issue be water in the gas from where I cleaned my tank? I see a very small layer in the separator and have emptied the bowl several times. I am just trying to figure out if the carb is still having an issue or if its just water in the gas.


Thanks
Andy

[Eugene]

Try "Heat" or other name brand of alcohol that mixes with water in fuel. The engine will burn the gasoline/Heat mix.
Available at auto parts stores.

Heat will also dissolve ice buildups in the fuel system.

[Don McCombs]

When you rebuilt the carburetor, did you remove and clean the filter screen in the 90-degree brass fitting between the Zenith carb and the fuel line?

Also check the fuel tank outlet for any residual debris.

[72chevelle]

Don, I did clean out that screen.

Here is a video of what it’s doing.
https://youtube.com/shorts/uKHn1rL8EOw?feature=share

[Don McCombs]

Looks to like when you think you are opening the choke, you are actually closing it. Watch the plate as you move the choke rod. What year is this tractor?

[72chevelle]

Looks to like when you think you are opening the choke, you are actually closing it. Watch the plate as you move the choke cable/lever. What year is this tractor?

Its a 1965. The Carb is not stock its one I got a long time ago that someone said was an upgrade for these models. I did confirm that the blades were closed when choke was on and running and as soon as I opened the choke the blades opened and engine dies

[Don McCombs]

Did you check the tank outlet hole for debris? Another possibility is the vent in the fuel cap being plugged. Remove the cap and try starting/running it.

[72chevelle]

Did you check the tank outlet hole for debris? Another possibility is the vent in the fuel cap being plugged. Remove the cap and try starting/running it.

I did remove the cap because the crossed my mind as well. I can see the fuel filling the bowl when I take it off and empty it and its running pretty quick (fills withing 10-15 seconds) I am really leaning toward this carb being bad. The amount of junk when I took it apart was pretty bad. I pulled all the jets and cleaned them but I just dont trust it. I have a new carb (the correct one) from Steiner coming soon.

[staninlowerAL]

.......I have a new carb (the correct one) from Steiner coming soon.

There are several carb repair specialists on the forum (Don is one). Keep your old carb, it can probably be repaired.
Edit: Don is located in Deep Creek MD, not too far away.
Edit: Did you try blowing back into the tank through the sediment bowl? There is not a straight passage through the valve so you cannot run a wire through the passage.

[Don McCombs]

Your description of the symptoms definitely point to a fuel restriction somewhere. Either in the carburetor or before it. Stan's suggestion of blowing back through the sediment bowl is a good one. Before I replaced the carb, I would try a puff of compressed air back through the fuel line, into the tank. Look for new debris after this procedure.

[72chevelle]

Your description of the symptoms definitely point to a fuel restriction somewhere. Either in the carburetor or before it. Stan's suggestion of blowing back through the sediment bowl is a good one. Before I replaced the carb, I would try a puff of compressed air back through the fuel line, into the tank. Look for new debris after this procedure.

I actually was able to try this and it didn’t help. I went through and ran a fuel line from my outboard boat tank I have as well and it was identical so I’m guessing it’s in the carb. Not sure where it would be.

[Glen]

Hi,
You didn't say if you cleaned the main jet.
The main jet can be plugged, then the engine doesn't get gas, or if it's partly plugged, not enough gas.
It's one reason you would need to have the choke on to run the engine.

Many times the carb also needs cleaning, and the float level set right.
They can have plugged passages inside them.
If the engine doesn't run right, and you think it's the carb causing it, I would take the carb apart and clean it, and set the float level.

Clean the outside of the carb with solvent before taking it apart, to keep dirt out of the carb.
Clean inside the carb with carb cleaner, or soak it if you have equipment for that.
Blow out all the passages with compressed air. Wear your safety goggles when using the air.

Below is a page from the Cub service manual, it shows setting the Zenith float level in the lower pic on the page.

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

Below are pages from the Cub parts manual showing the Zenith carb.
It says they were used on engines serial number 312390, which was made during 1975, and above.

The main jet is under the cover, number 18 in the pic, which is at the lower rear of the carb.
The main jet is number 20 in the pic.
The jet screws out, if you need to remove it. They have said on here to use a screwdriver that fits the slot well, and don't let it slip. Grind a screwdriver to fit well in the slot if needed.

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

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

There is originally a screen in the 90 degree gas line fitting at the carb, they have said remove the fitting to clean the screen.

[Clemsonfor]

Try "Heat" or other name brand of alcohol that mixes with water in fuel. The engine will burn the gasoline/Heat mix.
Available at auto parts stores.

Heat will also dissolve ice buildups in the fuel system.

If he is useing ethonol fuel it's basically got that already in it. Or you could just buy a few gallons of ethonol fuel and add too it. It will "soak" up any residual water and engine will burn it.

[Eugene]

If he is useing ethonol fuel it's basically got that already in it. Or you could just buy a few gallons of ethonol fuel and add too it. It will "soak" up any residual water and engine will burn it.

Initial post:

evaporust in the tank for a day and drained it and rinsed it with water, then with gas. Could my issue be water in the gas from where I cleaned my tank? I see a very small layer in the separator and have emptied the bowl several times. I am just trying to figure out if the carb is still having an issue or if its just water in the gas.

[ricky racer]

It sounds to me like there is a blockage somewhere in the carburetors jets. If it runs with the choke on, that tells me it will run on the fuel it has, even if there's some moisture in it. With the choke closed, more fuel is drawn into the engine. With the choke open, more air is introduced which leans out the fuel mixture to the point that it won't run. The problem appears to me to be either lack of fuel flow to the carburetor or more likely a restricted fuel passage within the carburetor.
Have you tried opening up the idle screw a bit? Possibly its screwed in too far. I'm not familiar with the Zenith carburetor but typically the idle screw on most carbs get turned out around 1-1/2 turns.