B&S Ignition


Staff member
My wife's mower wouldn't restart when she stopped it for a few minutes. I determined that there was suddenly no spark (starting fluid, looked for spark with new plug). This is an extremely simple "ignition system", just a coil with flying-magnets on the flywheel and the spark plug. Yeah, there is a kill switch, but I disconnected it right at the coil, no joy. I checked continuity of the HV lead and the primary/secondary coils, all seemed good. I reluctantly bought a new coil ($40+!) and installed it. I still had no spark at a test plug with that, but started wondering if I was spinning the engine fast enough to see it (spinning with plug out and a speed-wrench on the crank/flywheel nut). Well, I "played along with it" and finished assembling and it fired on the first pull. So, my wife resumed using it and it died again after about 15 minutes. I got it to start again and watched it run briefly and sputter to death; no spark again. No visible spark, and no joy with the starting fluid. I am open to suggestions as to what to look for. Photos of the (old) coil are attached.


Hoping it this simple -
This side out ? you should see that on coil
Air gap coil to 'flywheel'... was there a gauge with new coil?

Have you tried a new plug... ?
Last edited:


Staff member
No gauge, I set the air gap in the .005-.010" range. The coil is marked "cylinder side", little chance of getting that wrong. In testing for a spark I use a new plug (and get no spark), but haven't tried running with a new one. I'll give that a try. The flying-magnets are on the OD of the flywheel and fully visible; no damage that I can see.
I think cyl side goes down, you should not see that - read other side I think it says this side up...... but that all sounds screwed up unless someone switched it IDK


Staff member
Well, you can read it before you install the coil... The original coil is labelled on both sides ("Up" and "Cyl side"), you are right about that.
only thought I have is new coil may not be good, maybe ohm coil, OR a really bad plug but I am sure you have installed a new one...


Staff member
This one is on "hold" for a while, hopefully near-infinite like the Korean War. I went to breathe life into her back-up mower (will be subject of a different B&S thread!) and tried to start this one while I was at it. It fired on the first pull and she continued to use it for the next two hours or so; complete with several re-starts due to moving it in the yard and re-fueling. It was the same old spark plug but still has the new coil. If I am dumb, I will check for spark again now, it seems like there may be something lacking in the way I am doing that. If I am really dumb, I will also swap back the old coil and see if it runs...


Wrench. I help when I can
Bill, I think my buddy Jean Guy has one of those. I really don't think you are dumb. Quite the contrary.

Here is a video of how I do it.

Maybe it will help.

The guy in this video uses a business card, I use a match book folded in two. It works for mopar CKP sensors and air gap is spot on.

Do not even need to take out my feeler gauges.

Can you tell me what year this B/S is and what size cc?

Here is the link



Wrench. I help when I can
My old lawn boy had same problem. Smoked a cigarette and folded my match book.

That lawn boy ran all summer.

Only thing really crazy, was that big damn dog that shit everywhere.

When I took out the snow blower, that shit had been frozen all winter and when it flung out of the chute, broke my kitchen window. I was not a happy camper.

Tried to get paid buy said owner of dog. He just laughed, revenge is often not a good thing. So the other winter long, I saved all his dog shyte in a 2l yogurt tub.

When it started to smell rotten, he asked me If I had put that there under his doorstep.

Yep, 100%

How do you feel me now?

I was scared of him, he was a beefy guy. Funny thing, he told me that small ppl like me are the most dangerous. A few Heineken later, he said I would not want to play with a agile guy like you. I just said, if I stand still long enough, I am done, my head is off my rocker.

Jim Fairbanks from new york that shoots coons, he probably gets my drift.


Wrench. I help when I can
Safe to say, that guy asks on me now.

But he still scares me.

I had to choke him out with a rear naked choke.

Not easy when your 5 foot 7 inches tall. This guy is at his best when he is something like 6ft 4.

When he got conciseness, he asked what happened.

I said, you scared me, and I jumped on you like a monkey, and you passed out while I pressed the jugular.

He asked me how did I choke him? I just told him I used his left arm to choke himself. He laughed, he said that I used his body against him. Yeah, pretty much that.

Lesson to ones self, technique always over ego.

Like playing chess.;)
As rusty looking as that coil is, I wonder how well the safety bale is working. Typically if the mower is left outside the weather gets down in the cable and makes it hard to pull. In short the cable stretches and doesn't pull the kill switch far enough to stop shorting the coil out. Had it happen on a mower I owned, and one I fixed for a friend.



Staff member
I disconnected the kill circuit, right at the QD spade on the coil, to eliminate any possibility of a short in the wire or an inop switch; did that right at the beginning of my trouble-shooting process.


Wrench. I help when I can
did that right at the beginning of my trouble-shooting process.
Did it run for a good meaningful time??

Was she jamming up the mulch and just disregarded the factor? I really don't want to think I think poorly of your wife.

But I am very sure this is a future fixed issue.



Staff member
I don't think this is truly fixed, just hoping it is at peace with me for a long time. It ran for about 2 hrs. after it magically healed itself. Trust me, she knows when it is loaded up. Besides tall weeds, she has stalled mowers hitting rocks, bricks, chain, pipe, birds, dirt humps, etc. Over the years I have straightened several cranks and bushed/replaced main-bearings on that drive end of the crank (many different mowers). Her job is too mow, my job is to keep the mowers running...