To-20 Marvel schebler Carb rebuild

Wesh1013 · Nov 24, 2022

Hello all,

I have a 1950 Ferguson to-20 with the Marvel-Schebbler carb, I rebuild it and set everything according to the owners manual, 7/8 turn for the idle jet and 1-1/4 for the main jet, the tractor would start and run for a little bit, about 30 seconds and then shut off, a few days later I tried to start it again and it would give a few puffs and then nothing, and now I can't get it to fire at all. No ot sure what is going on or what the problem would be and I would appreciate any help. I also changed the spark plugs and put new plug wires on and changed the oil, also changed oil in the air cleaner. Today when trying to start it and messing with carb I had gas pouring out of the side of the carb. And I'm not sure why I would get that.

This post was edited by Wesh1013 on 11/24/2022 at 09:27 am.

Bruce(OR) · Nov 24, 2022

Sounds like you got the base settings correct.
Remove the inlet brass piece where the fuel line goes in and make sure that screen is not plugged.
Pull the bottom plug out of the carb and check your fuel flow through the unit.
You can also install a barbed fitting with a pice of clear hose, open on the far end,
Hold it up, turn on the fuel flow and the fuel level inside the clear hose will show you where the fuel level is inside the carb.
If it was running good after the rebuild and then went south, you have one of two possibilities.
(1)Float went bad, filled with gas and is sinking, unable to turn off fuel flow.
(2)dirt in the float circuit holding the fuel inlet valve open.
You can also try rapping the side of the carb with a large plastic screwdriver.
That might dislodge you debris.

Steve@Advance · Nov 24, 2022

Have you checked the spark quality at the plug end of each wire?

It should make a minimum 1/4 inch spark to ground at the plug end. Check
each one to be sure they are all firing.

Having some fuel drip out of the carb following a failed start is normal.
Having it continue to drip continuously is not.

Have a clean glass ready, open the fuel tank valve, remove the drain plug
from the bottom of the carb. catch the flow, see what you catch. There
should be no water, minimal grit or trash. The flow should remain strong,
not slow to a drip or stop. If there is water or trash, the tank will
need to come off and be dumped and rinsed out with E85 gas. If it's rust
flaking, the easiest fix is a new tank.

It only takes a tiny speck of debris to hold the needle valve open and
make the carb flood. Trying to operate with a dirty or rust flaking tank
is nothing but frustration!

Wesh1013 · Nov 25, 2022

Thank you for the suggestions, I took each spark plugs back out and checked the gap, each one was correct and I was getting spark on each. I have a strong gas flow but I will be looking into replacing the tank as it's the original, and I do get a little bit of debri from it, the tractor ran alright before I rebuilt the carb, it just didn't run as good as it should, I took the carb back apart and will be testing the float with hot water to see if it is still good, the last time I turn the gas on I had a lot of gas coming out of the side of the carb where the top and lower half mate, I flattened the surfaces And will hope the gasket seals correctly when I put it all back together. I had gas flow back into the air intake tube so that tells me the float might be bad since it wasn't shutting the fuel flow off. Would adding an inline fuel filter hurt or will it restrict my fuel slow to much? Still Have a lot to learn about these old tractors.

Jim L WA · Nov 25, 2022

Hi Wesh1013, welcome to the forum.
The float can be good, but it's the needle and seat that have to stop the gas flow. Make sure the seat is screwed down tight.
The reason Steve mentioned the 1/4 inch spark is to test for a weak spark It's easy for a spark to jump a .025 gap out of the engine, but if the spark is weak it won't jump that under compression. But, it sounds like your problem is carburetor related right now.

Bruce(OR) · Nov 25, 2022

It has been my experience that in line filters tend to stop the flow. Now if you use and in line filter that is a screen style instead of paper element, you might not impeded the fuel flow. However the fuel line inlet fitting into the carb should already have a screen in it.

Mad Farmer · Dec 9, 2022

As mentioned I'd be focused on the float and inlet needle/seat. Besides being tight make sure you didn't forget the gasket.

Bruce's mention of checking float level using a screw-in nipple and clear tubing will tell exact level of gasoline in the carb. That method is also mentioned in the service manual. Should be able to get a nipple at a good hardware store.

I've been working on a TSX 361A. The parts manuals have better pictures than the service manual. I can the other carbs if you have a different one?

This post was edited by Mad Farmer on 12/09/2022 at 01:27 pm.

Wesh1013 · Dec 11, 2022

Just giving an update, first of all, I
appreciate all the input and responses, I
would have been lost without them. I took the
carb back out, the main running jet had
clogged so I cleaned everything really good
again, and changed the jets, the first
rebuild kit didn't come with them, put a new
float in, filed the two mating surfaces of
the the top and lower half to ensure they
were flat, put everything back together, put
a new fuel screener in and change the screen
and gasket in the sediment bowl and it's
running better than it ever has in my
lifetime, was grandpas, he bought it brand
new, I'm sure it could be running a bit
better, still figuring carbs out.

Jim L WA · Dec 12, 2022

Wesh1013, thanks for the update. Good for you for getting it running so well.
Don't be a stranger on here. You have experience to help others in the future.

To-20 Marvel schebler Carb rebuild

Wesh1013

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Bruce(OR)

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Jim L WA

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