Allis B runs rough and kills when hot.
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=211990
Printed Date: 17 Sep 2026 at 4:38pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: Allis B runs rough and kills when hot.
Posted By: Hillmann
Subject: Allis B runs rough and kills when hot.
Date Posted: 14 Aug 2026 at 9:15pm
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I have an allis B that after about 30 to 40 minutes of working begins to run rough and eventually stalls. It restarts right away but continues to run rough. This is a new problem that has only happened the last 3 times I used it. A couple things about the engine that may be important: it is in rough shape, it burns a quart of oil in 2-3 hours of working hard. It has a known good condenser from anothe tractor,and the problem continues, the govoner doesnt really wprk. Any suggestions on where to start troubleshooting? My first guess was the condenser was bad, my next guess is carbon may be building up on the heads and causing pre detonation, but I dont know if that is a common problem on these engines and dont want to pull the head if there are more likely problems that I should look at first. |
Replies:
Posted By: steve(ill)
Date Posted: 14 Aug 2026 at 10:40pm
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my first guess would be the COIL.. How old is it ? Is it a 6v ? Is the tractor 6 or 12v ? You said condenser, you have a Distributor ?? not a Mag ? Engine can also vapor lock if fuel line gets hot.... or run out of fuel if gas cap is not vented.. Can you loosen the cap when it dies and see if that helps ?
------------- Like them all, but love the "B"s. |
Posted By: Les Kerf
Date Posted: 14 Aug 2026 at 10:59pm
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How long has it been since the valves were adjusted? |
Posted By: Hillmann
Date Posted: 14 Aug 2026 at 11:05pm
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It has a magnito. I run it with the gas cap loose to prevent a vacuum forming in the tank. Once it stalled out today, I removed the sediment bulb to check if fuel was flowing. It was not obstructed. I did not remove the plug on the carb to make sure fule was flowing into the carburator (I was in the woods and didnt have any tools) Maybe I will try to replace the entire magnito with a known good one tomorrow, if the problem persists I will know ot isnt related to the ignition. |
Posted By: Hillmann
Date Posted: 14 Aug 2026 at 11:09pm
| 2 years ago. It has seen very little use since then, so maybe 30 ish hours. I will swap the magnito and make sure fuel is flowing through the carburator, if neither of those are the problem I will check the valves. |
Posted By: steve(ill)
Date Posted: 15 Aug 2026 at 8:33am
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the mag contains the condenser and a coil.. If the coil is the old black tar coated original unit, that could be a problem... If it is a red plastic one, it is newer, but could still be a problem if you dont find another cause... The condenser is a common problme.. It is possible that a NEW condenser fails.. They dont make em like they use to.. If you have another mag, that is a great idea... Narrow down that it is inside the mag.... A new condenser is cheap and would be the first test... then the coil. ------------- Like them all, but love the "B"s. |
Posted By: Les Kerf
Date Posted: 15 Aug 2026 at 10:58am
I have made the mistake of not letting the fuel flow out the bottom of the carburetor long enough to verify that there was adequate continuous flow; three minutes of steady flow should be sufficient.
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Hillmann wrote:Posted By: Hillmann
Date Posted: 15 Aug 2026 at 2:34pm
| I am working on the tractor today. Driving ot out of the woods it appears to be starving for fuel. I had to keep ot half choked to get to wher I cam work on it. Once I was able to work on it(5 to 10 minutes of running) the carburator is too hot to hold on to. |
Posted By: wjohn
Date Posted: 15 Aug 2026 at 3:29pm
I know I've said this many times on the forum, but for the OP's benefit... I once had a dead moth that didn't quite float to the top and didn't quite sink to the bottom of gasoline, and that was a fun one to finally get figured out. I would second the 3 minutes figure. Of course catch and save all of it. ------------- 1939 B, 1940 B, 1941 WC, 1951 WD, 1952 CA, 1956 WD-45 |
Posted By: Les Kerf
Date Posted: 15 Aug 2026 at 4:09pm
Hmmm... intake valve sticking open a bit might let some hot exhaust blow back through the carburetor, causing it to run rough and heat up the carb
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Posted By: steve(ill)
Date Posted: 15 Aug 2026 at 7:34pm
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check the radiator to make sure it is full of antifreeze.... when you get it running right, buy a small inline fuel filter for a lawn mower and install with a hose from the sediment bowl to the carb.. ------------- Like them all, but love the "B"s. |
Posted By: Hillmann
Date Posted: 15 Aug 2026 at 9:13pm
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I adjusted the valves, most had way too much play. While i had the hood removed and had easy axcess I removed the carburator, took it apart and cleaned it. When I put it back together it ran fine. I assume something was blocked in the carb and the valves had nothing to do with it. When I had the muffler removed to get the hood off, I saw that the bottom of the exhaust manifold is rotted out and there are 3 or 4 spots where exhaust is blowing at the carburator. I need to figure out some type of heat shield to direct the hot exhaust away from the carb. |
Posted By: Les Kerf
Date Posted: 15 Aug 2026 at 11:12pm
Yikes!  You need a new manifold my friend
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