Farm Equipment - Allis B running weird

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Allis B running weird

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=207948
Printed Date: 13 Oct 2025 at 2:04pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

Topic: Allis B running weird

Posted By: Ttague39B
Subject: Allis B running weird
Date Posted: 26 Aug 2025 at 12:06pm

Hi, I have a 1939 allis chalmers b that is idling fine, but as I start driving it it wants choke to run. The ajustment screw is nit changing anything, (im running it on a zenith carb full metal needle) and the other day when I went to start it it kept stalling after moving 10 feet, but would restart fine. A few days later it idled for about 15 minutes great, then went to move it and stalled right out. Any ideas or thoughts? Thank you.

Replies:

Posted By: Straanger
Date Posted: 26 Aug 2025 at 4:51pm

How old is the fuel? When was the last time you cleaned the carburetor?

Posted By: Ttague39B
Date Posted: 26 Aug 2025 at 4:55pm

Fuels maybe 2 months old, non ethanol, its only been a year, maybe two.

Posted By: steve(ill)
Date Posted: 26 Aug 2025 at 5:39pm

main jet plugged......... choke on means lack of fuel..

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Like them all, but love the "B"s.

Posted By: Orange B
Date Posted: 26 Aug 2025 at 5:39pm

hi, sounds like there is a blockage in the fuel line due to dirt either floating around in the tank , fuel line , or the screen in the fuel bowl. I have had that happen in the past on my 48 b. I would take the fuel line off at the carb see if the fuel flows freely , if not work towards the tank a section at a time till you get a free flowing line .

Posted By: Sugarmaker
Date Posted: 27 Aug 2025 at 6:09am

39B,

As others have suggested check for good fuel flow. I just had our freshened CA do something similar. Fuel was flowing good. It was the condenser in our CA! Yep sounds strange but it had no power ran only at idle and very rough! Might be worth a thought as you do trouble shooting on your B.

Looking forward to your updates.

Regards,

Chris and Cheryl

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D17 1958 (NFE), WD45 1954 (NFE), WD 1952 (NFE), WD 1950 (WFE), Allis F-40 forklift, Allis CA, Allis D14, Ford Jubilee, Many IH Cub Cadets, 32 Ford Dump, 65 Comet.

Posted By: Rick of HopeIN
Date Posted: 27 Aug 2025 at 7:29pm

I have had so many issues that turned out to be just old fuel gumming up float valve or a carb passage. Had a bad magneto long ago on my B but it only acted up when it got good and hot. Luckily a guy up the road rebuilt magnetos at the time and got me back up and running.

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1951 B, 1937 WC, 1957 D14, -- Thanks and God Bless

Posted By: Jim2
Date Posted: 29 Aug 2025 at 8:07am

Have a 1940 Allis B here with similar problems. Mine starts and idles fine. I'm running the Zenith carb with the needle screwed all the way in to the seat. If the needle is out at all, it needs choke to idle nice.

I can idle up 3-4 notches before it starts to stumble, but after that need choke for it to run well. It does pull really well with a little choke. I've had the carb apart 3-4 times 2 years ago and replaced most all of the parts including throttle shaft and choke butterfly shaft with a kit from Steiners.

This year saw an ad on Craigslist from a local guy that offers ultrasonic carb cleaning. Took the carb to him, and he looked it over. He thought a dunk in his ultrasonic cleaner would be a waste of time because it had all new jets and everything is clean inside.

I've been trying to figure out what might be wrong. I know that Steve says main jet has to be plugged, but don't think that is the case here. Have seen a couple of guys online talking about internal air leaks in older Zenith carbs. The ones I saw were aluminum-body carbs that warped. Symptoms they describe seem very similar to what I'm experiencing here. The suggest sanding the body where the split is to remove the air gap. Have tried that, but being cast iron don't think that was the problem necessarily.

The venturi doesn't seem to seat particularly well. . . . Wondering if there could be some other place where there is an internal air leak?

Tractor runs OK, and I can get work done with it--just getting tired of continually adjusting choke whenever I throttle up or down. Thinking about buying a new carb online, but wondering if I'll just have other problems down the line as likely Chinese and may have other flaws? Old, used carbs on ebay don't look even as good as what I'm running, so hard to believe they would give me anything but more problems.

Not much help, right?

Jim

Posted By: steve(ill)
Date Posted: 29 Aug 2025 at 12:33pm

JIm, if you use the CHOKE, then you normally have a lack of fuel.. Its possible that way back when someone put the wrong main jet in and it is too small.. or the carb was off another model tractor and used a smaller main jet..

I bought one of them chineese aftermarket carbs for $30 or so 3-4 years ago.. If would not run about 1/2 throttle unless you used the choke.. Decided it needed MORE GAS.. so i drilled out the main jet about .002 inch ( that made the cross sectional area 10% larger and therefore 10% more gas........ and that helped 90%.... Thats what i use now.. And your right, its not PERFECT... but works out pretty good.

and your right... an AIR LEAK ( too much air) is the same as Lack of FUEL.

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Like them all, but love the "B"s.

Posted By: Jim2
Date Posted: 29 Aug 2025 at 1:23pm

Went to talk to a local guy that works on tractors. Described the situation and he suggested trying a new carburetor, so have one coming. Said he'd take a look at it if the new carburetor didn't help, but he thought it would.

I put a new kit in the carburetor that's on there now. Carb I'm running has all new jets, float valve, throttle shaft, choke shaft, etc. Figured it's time to try something else.

Jim