Allis Chalmers B carburetor question

[ENC-AC]

Hello all,

I'm new to Allis Chalmers and recently inherited a 1948 Allis Chalmers B and working to restore it. The tractor has a Marvel Schebler TSX154 carburetor on it that I've rebuilt using the complete rebuild kit from Steiner.

My question is how should I adjust the throttle plate? I don't know if I have it adjusted correctly and I'm having an issue where the tractor will only run if I have the choke on about half way.

Any guidance anyone can provide would be greatly appreciated. Thank you!

 

[old]

Most of the time if you have to have it choked to run that means a passageway in the carb is still clogged up a bit. When you rebuilt the carb did you use a piece of wire or as I do a torch tip cleaner tool to poke out all the passageways

 

[wore out]

It's a good idea to center to center the throttle plate, but that likely won't solve the problem you are having.

Centering the plate affects idle and just off idle/transfer circuits the most.

Back off the idle speed screw, then loosen the throttle plate screws and move the throttle plate so it fits centered in the bore and look through the bore at light to verify that it fits against the bore all the way around, then tighten the screws (possibly using a little Loctite) and then screw in the idle speed screw enough so that the throttle plate doesn't bind, then make the final idle speed setting with the engine running.

 

[ENC-AC]

(quoted from post at 10:54:34 12/07/23)
It's a good idea to center to center the throttle plate, but that likely won't solve the problem you are having.

Centering the plate affects idle and just off idle/transfer circuits the most.

Back off the idle speed screw, then loosen the throttle plate screws and move the throttle plate so it fits centered in the bore and look through the bore at light to verify that it fits against the bore all the way around, then tighten the screws (possibly using a little Loctite) and then screw in the idle speed screw enough so that the throttle plate doesn't bind, then make the final idle speed setting with the engine running.

I apologize for my questions since I'm a newbie, but when you say idle speed screw, are you referring to the adjustment screw on the throtle shaft?

 

[ENC-AC]

(quoted from post at 10:47:14 12/07/23) Most of the time if you have to have it choked to run that means a passageway in the carb is still clogged up a bit. When you rebuilt the carb did you use a piece of wire or as I do a torch tip cleaner tool to poke out all the passageways

Yes, I am pretty certain that all passageways are clear. I soaked the carburetor in carb cleaner twice, each for 2 days straight. Then blew out the passageways and brushed everything before putting it back together with the new parts.

 

[wore out]

I apologize for my questions since I'm a newbie, but when you say idle speed screw, are you referring to the adjustment screw on the throtle shaft?

Yes.

 

[Bob Bancroft]

The only reasons to remove the throttle shaft are if it is noticeably worn, and/or to replace the seal. Did you install a new
seal with the lips facing out?
You have good instructions on centering the throttle plate. Know that the edges are tapered, so it only goes in correctly one
way. And I agree with old, you probably have other problems.

 

[ENC-AC]

(quoted from post at 12:20:26 12/07/23) The only reasons to remove the throttle shaft are if it is noticeably worn, and/or to replace the seal. Did you install a new
seal with the lips facing out?
You have good instructions on centering the throttle plate. Know that the edges are tapered, so it only goes in correctly one
way. And I agree with old, you probably have other problems.

Yes, I replaced the seal when I replaced the throttle shaft. I noticed right away that the throttle plate had to go only one way so I feel pretty confident now that I have that right based on your's and old's comments.

I do intend to replace the fuel line next because there was an old bend in it that i've tried to straighten out and not sure if that is causing an issue with gas flow to the carburetor.

 

[old]

Air and carb cleaner while it helps a good bit if you don't use a wire or some such thing to poke out the passageways you will leave things behind that will cause the problem your having. Learned that years ago so I keep a torch tip cleaner tool in with my carb tools so I can clean out the passageways

 

[jimgraycase]

when I have to have the choke on halfway it usually means there is a vacuum leak somewhere and I have found that replacing the
carb tom intake gasket fix's the problem 9 out of 10 times

 

[grandpa Love]

Unfortunately the need for choke while
running means there is still a bit of
blockage in the carb...... Another slim
possiblity is the manifold gasket is
leaking, a shot of carb cleaner around it
should give you the answer..... Tractor
running, carb cleaner should make it rev
up.

 

[ENC-AC]

(quoted from post at 07:47:36 12/08/23) Unfortunately the need for choke while
running means there is still a bit of
blockage in the carb...... Another slim
possiblity is the manifold gasket is
leaking, a shot of carb cleaner around it
should give you the answer..... Tractor
running, carb cleaner should make it rev
up.

I have replaced the manifold with a new manifold and new manifold gasket. The old manifold had rusted so bad that there was a leak.

I'll tear into the carb again and go thru all the passageways just to make sure all is clear. Thank you all!

This post was edited by ENC-AC on 12/08/2023 at 07:27 am.

 

[mdm1]

Take a look at this page. It may help some. https://route249.com/2018/09/09/how-to-rebuild-the-marvel-schebler-carburetor/

 

[Bergmann]

I experienced similar behavior in a slightly different Marvel Schebler carb rebuild and I believe replacing the plastic venturi that came with the carb rebuild kit with a metal venturi made the difference. I paid a premium. If you continue to struggle with performance, you may want to look into the different venturi styles available for this carburetor. Carbs Unlimited was a good vendor online for me. Good luck.