Farm Equipment - Weak Spark on B

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Weak Spark on B

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=176011
Printed Date: 29 May 2025 at 2:05pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

Topic: Weak Spark on B

Posted By: LittleB
Subject: Weak Spark on B
Date Posted: 15 Nov 2020 at 7:11pm

I've been having trouble with a couple of annoying problems with my B. Lately I have had difficulty getting it rolling along even after it warms up. If I don't feather the clutch a bit starting out in 2ND it has a tendency to stall. It will run okay for a bit, then start running rough. It now has become difficult to start. I thought to remove the plugs then move it around to the fire position on the flywheel. I held on to the #1 plug wire, then cranked it to trigger the Mag. It seemed to me that the charge was only just slightly noticeable. Will this low voltage cause my first problem and what can I do to alleviate the low voltage as it seems problemic.

Joe

Replies:

Posted By: steve(ill)
Date Posted: 16 Nov 2020 at 8:33am

the magnito works with a COIL and a CONDENSER inside, that fire when a contact POINT opens and closes... When a mag gets old you can loose spark if the CONDENSER goes bad.. You can have a WEAK spark or loss of spark when HOT if the COIL has an internal problem..

If you are sure you dont have a carburetor / fuel problem, then a replacement of the COIL and CONDENSER might be next. You can buy them on line from several vendors.. The POINT is what opens and closes and lets the system SPARK.. The point can tarnish on the contacts and eliminate the spark.. Cleaning the point contacts is a good idea. Normally the point is working, or not... and does not work "sometimes".

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

Posted By: steve(ill)
Date Posted: 16 Nov 2020 at 8:40am

https://www.youtube.com/watch?v=2fmnP700qXc%20" rel="nofollow - https://www.youtube.com/watch?v=2fmnP700qXc

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

Posted By: Eric B
Date Posted: 17 Nov 2020 at 9:42pm

When you did your "spark observation" was it in broad daylight or with subdued lighting? In bright light it's not that easy to evaluate the true strength of the spark. Tired spark plugs or incorrect gap can also contribute to the kind of symptoms you mention.

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Currently- WD,WC,3WF's,2 D14's B. Previously- I 600,TL745,200,FL9,FR12,H3,816 LBH. Earth has no sorrow that Heaven cannot heal!

Posted By: Dick L
Date Posted: 18 Nov 2020 at 5:31am

Dirty points is another cause of weak spark. It could be a weak spark but sounds like it could be a fuel delivery problem some where between the tank to the intake manifold.

Posted By: LittleB
Date Posted: 18 Nov 2020 at 6:09pm

I've replaced the points, condensor, rotor and plug wires recently. What I have found is that when I modified the length of the wires I may have messed up the metal ends that plug into the magneto. I corrected this. Now it starts better and seems to run better, so the next thing will be the test drive.

Joe

Posted By: jlbintn
Date Posted: 20 Nov 2020 at 8:39am

Echo the sentiment that spark may be hard to see in bright conditions. I have some recent experience with this type of issue, after having the head rebuilt, new valves, the whole works. Put a reman starter on the tractor as well, then had trouble starting the damn thing.

Tore the magneto completely down, cleaned it, installed a new bearing, points, condenser, coil.... but I believe something else was wrong in the magneto. I could never get it to spark, so gave up and bought a rebuilt magneto.

It arrived yesterday, installed it on the tractor, and it fired up right away.

I don't know what I could have done wrong with the magneto, I'll attribute some of it to inexperience, but it really wasn't that hard to tear it down, clean it and put it back together.

Good luck.

I also rebuilt the carburetor over the summer, your problem could be in the carb somewhere.

Posted By: jlbintn
Date Posted: 20 Nov 2020 at 9:05am

I forgot to mention: Before I put the new magneto on the tractor yesterday, I tested spark on all connections on the distributor cap.... saw spark on every one, even in bright light.

fwiw

Posted By: DaveKamp
Date Posted: 22 Nov 2020 at 9:31pm

Seeing a spark in the air, and having a spark in a compressed mixture inside a combustion chamber are two totally different circumstances.

A magneto not only has points, condenser, and coil, it has armature timing... aka 'phasing'. When the armature's magnet goes through it's swing, the points must open at the proper ARMATURE ANGLE, in order to have the proper field collapse for an intense discharge.

Also... when a magneto generates it's output, it does so under circumstances where a slight 'leak' of energy across the plug insulator (caused by a little carbon) can cause the spark intensity to fall off substantially. This is called 'carbon fouling', and it will come and go depending on mixture and insulator temperature.

Oftentimes, the insulator's face has been eroded, and is protecting a carbon 'film' on the insulator surface. Sometimes, the plug is simply not hot enough to burn off soot that has accumulated on the insulator.

One of the earmarks of carbon fouling, is that the engine will seemingly run fine, but drop out at any attempt to throttle up... but once the engine is really good and warm, you can gradually bring the throttle up, and once it's worked a bit, it will settle down and be happy... but if you idle it for a long time after, it'll fuss and spit when trying to throttle it back up.

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Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.