Testing B&S Coil

golodkinApril 18, 2014

A blade trimmer that has worked flawlessly for years suddenly stopped working and gets no spark from the coil lead.

The 2 HP B&S engine is a 60102 and the coil is exactly like this one:


There are three leads: One to the spark plug, one to the points and a twisted pair of magnet wire from the coil going to ground.

The magnet seems extremely strong.

I want to test the coil and see if it's the problem, but the information I've found online so far is 180� contradictory.

DC resistance between the spark plug cable and ground is a steady 3000 Ohms. Depending on who you believe, this means either it's perfectly good or it's stone dead. Helpful, huh? Presumably, they're talking about different coils, but they don't clarify.

To get to the lead going to the points, I have to pull the flywheel, which I'd rather not do if I don't have to.

Any suggestions as to how to test this coil and where to go from here?

If the above info indicates that this is indeed a dead coil, is it possible to retrofit a new electronic ignition coil to this model?


Here is a link that might be useful: Example of coil

This post was edited by golodkin on Fri, Apr 18, 14 at 19:28

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The coil example shown is a coil that is electronic ignition. With the type number also, we could look up that info. Breaker points momentarily ground on coil wire to release the spark. On electronic ignition, like the one on Ebay- they have a small capacitor and you would see the small pickup on the inside of the coil. Both will have a kill wire which when grounded, doesn't allow the coil to release spark to the spark plug. So in answer to your question, test those things rather than testing the coil. It is easy, cheap and more reliable than a coil test. Or the replacement coil may be electronic ignition where you just clip the point wires and have a stronger more accurate spark. Again, model and type would be best.

    Bookmark   April 18, 2014 at 10:37PM
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Yes, just get a newer style coil off of a junk 2-4 horse pushmower, snip the wires to the points, slap it on, hook up the kill wire, and you are done.

    Bookmark   April 19, 2014 at 12:36PM
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The Briggs breaker-point coil should ring out to about 5K ohms from plug wire to ground and 10-20 ohms from points wire to ground. To properly test the coil, you will have r&r the flywheel and disconnect the wire to the points/condenser. However when these coils fail it is usually the secondary which has more turns of finer wire. The primary (10-20 ohms) is much more robust.

I suspect you have problems with either the points or condenser, or maybe last time it ran you had a backfire causing the flywheel key to shear.

Unfortunately the Ebay listing isn't much help. Seller pictures show a breaker point coil (298502/395488) first and then a Magnetron (398593/496914) later in the listing. The Magnetron coil has a bulge on the carburetor side for the trigger electronics.

Agree with previous poster that easiest fix would be to replace with electronic Magnetron such as 398593. The cost about $35 for OEM and $25 for aftermarket. Another approach would be for retrofit electronic module 394970 to your existing coil. These are about $15.

In any case, I think you should remove flywheel and check condition of the key. If it is partially sheared, even a minor amount, it will play hell with ignition timing, and you will be chasing your tail.

    Bookmark   April 19, 2014 at 1:59PM
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Yes, I spent the entire day on the internet yesterday trying to find out if I could just put on a post-'83 coil on it, snip and secure the old primary wire, blow the whole mess off and essentially have a new electronic ignition system without pulling the flywheel, but naturally *NOBODY* would come right out and say you can do that.

I found generic Magnetron-type replacements for 793281 / 398593 / 496914 coils that fit 2-4HP horizontal-shaft engines with 2.5" armature mounts (which accurately describes the 60102, as far as it goes). I assumed that flywheels and blocks remained pretty much unchanged and this would be a slick retrofit, but I couldn't get any confirmation.

[Example: https://tinyurl.com/lcrs82w ]

So...I *can* indeed do this? Just clip off the old primary, mount and gap this new unit and call it done?

OK, it's ordered.

Two more points:

1: Can I still use the old sparkplug-ground kill thingy without blowing the new unit, or do I have to actually run a new to-ground kill switch wired to the bayonet fitting on the side if it?

2: I'm disinclined to open a new can of worms by pulling the flywheel because the unit was working perfectly at last use a couple of weeks ago and shut down normally at idle. A suddenly sheared key seems improbable. I have no (0) spark now, not a timing problem. If a simple coil upgrade doesn't fix it, then I'll pull it and see, and I'll still have an upgraded ignition system. The flywheel is as it came from the factory and has never been off, so I imagine it's about fused solid by now.

    Bookmark   April 19, 2014 at 4:50PM
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1. Spark plug kill strap will work OK with new Magnetron coil.

2. If you want to change the coil without checking the flywheel key, knock yourself out. It's your call. As for sheared key being improbable, I can tell you from 40 years experience, it's more common than you think.

    Bookmark   April 19, 2014 at 9:58PM
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A thing or two to add. A point type ignition will loose spark if the key is sheared where as an electronic ignition won't. Also, to check the key, you won't have to pull the flywheel- just the clutch. I wouldn't assume that all engines of your model have the same coil. That engine was built a good many years A type number would be helpful. The fact is you can't update all Briggs point ignitions with the new style coil. Thinking that your points are below the flywheel , you probably can.

    Bookmark   April 20, 2014 at 1:39AM
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How about when the coil is under the flywheel, like the old Tecumsehs with points. Can they be retrofitted to the electronic coil outside the flywheel?

    Bookmark   April 20, 2014 at 6:48AM
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baymee, I'd never say never- but it seems like some engineering would need to be done on that one. It could be a fun thing to know. Fashion up an adjustable mounting bracket and give it a try. Most of the Briggs w/o a point box can just have a cd coil popped on and life was better than before. No changing flywheels etc. A different scenerio- Kawasaki engines w/ a coil with a cd inside, the flywheel is different than if it had a separate igniter. In theory, one can replace breakers with an igniter- but they don't always work out. Someone smarter than me would have to tell you why...

    Bookmark   April 20, 2014 at 12:35PM
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Coil/armature arrived this morning in good condition.

Gapped/installed it, trimmer started on the second pull, ran maybe a little stronger than before with the better spark.

Hardest part was getting the crummy soft spark plug clip attached to the rock-hard ignition wire.

Didn't pull the flywheel, though the coil kit included what appears to be a flywheel key for for future use.

Thanks for the help!

    Bookmark   April 23, 2014 at 1:03PM
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