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Hi all - I'm new to this forum and this is my first post. I tried searching for my issue, and found some stuff helpful, but not what I was looking for. Hoping someone smart can assist....

I have a Craftsman flathead mower, built in 1993 (93101556), Briggs and Stratton L head model 124802-3230-01. I have never worked on it until this year when I finally took it apart to lap the valves, replace primer bulb, etc. Actually, I am surprised it still runs, given how little maintenance I have done on it. For a 24 year old engine, it has never failed me and the carbon build up was less than I expected.

My problem is not so much a problem, but a confusing issue. When cleaning up this engine and waiting for parts such as gaskets etc., I ran an ohm meter across the stop switch. I expected no continuity when the safety bail is held down (operating), and continuity when the bail is released (coil shorted to ground). But I have continuity of about 3 ohms....even when the contact points of the safety switch are open and continuity when the points are closed. Weird....the mower runs fine, and shuts off when the bail is released.

Whats up? First of all why is the engine even stopping when I release the bail? Is this because the brake is sufficient to stall the engine? (Kudos for B&S for a two part safety system I guess).

What am I measuring at 3 ohms here? Is it stator? Is my elemental knowledge of these stop switches correct, or am I missing something???

Thanks in advance guys. Any help appreciated.View attachment 31107

Pretend the stop switch is a hot wire, and were you have the meter lead is the neutral wire. Now if you run one lead on the hot wire or in your case the stop switch and the other lead to another part of the engine which would act as your neutral, you are completing the circuit, between the ignition module, the wire coming off of it going to the stop switch, through the tab were you have the meter back to the ignition module, the stop switch/tab is like opening the contacts on a switch.

Switches are to be completely isolated to test.

I hope you know how to clean all the lapping compound from the valves and seats after the lap job. If not you'll probably be ordering a new set of rings shortly.

ILENGINE said:

Pretend the stop switch is a hot wire, and were you have the meter lead is the neutral wire. Now if you run one lead on the hot wire or in your case the stop switch and the other lead to another part of the engine which would act as your neutral, you are completing the circuit, between the ignition module, the wire coming off of it going to the stop switch, through the tab were you have the meter back to the ignition module, the stop switch/tab is like opening the contacts on a switch.

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So is the 3 ohms I am measuring is the primary winding? The secondary winding reads 4.3 K, which I think is normal.

Thanks .

SeniorCitizen said:

I hope you know how to clean all the lapping compound from the valves and seats after the lap job. If not you'll probably be ordering a new set of rings shortly.

Click to expand...

I had a bad experience about 40 years ago with lapping because I obviously didn't clean it out properly, so you are right. Now I am super anal about it. Lots of hot soapy water. For every few secs lapping (which is all I have ever done), I probably spend an hour cleaning. Even one speck of compound remaining can be a problem. The valves themselves I just drop back in the Ultrasonic cleaner, but the head is too big

I don't touch my Hondas with lapping. If any of them had needed it (which they don't) they'd go to a shop to get done properly.

Thanks for the reminder.

CalgaryPT said:

So is the 3 ohms I am measuring is the primary winding? The secondary winding reads 4.3 K, which I think is normal.

Thanks .

Click to expand...

That would be the primary winding that has the low resistance. Don't over thing the resistance readings, Most people try to rely on the resistance readings, but for most applications can be ignored, because if it works, then don't mess with it.

I am having to deal with some of the new modules, on chainsaws, and blowers, that have spark advance, and over speed rev limiters, and you can have spark and still be bad.

ILENGINE said:

That would be the primary winding that has the low resistance. Don't over thing the resistance readings, Most people try to rely on the resistance readings, but for most applications can be ignored, because if it works, then don't mess with it.

I am having to deal with some of the new modules, on chainsaws, and blowers, that have spark advance, and over speed rev limiters, and you can have spark and still be bad.

Click to expand...

Thanks. I get it now.

Update as of a few hours ago. I had forgotten the the continuity feature on the older Fluke 73 series meters beeps for anything less than <150 ohms. Isolating things by disconnecting the kill wire from the mag and the switch proves the point. I was in fact measuring primary resistance in the coil by accident (aka stupidity). Once the switch was isolated, I saw what I my old brain thought should happen and had a Yeah Baby! moment.

Thanks everyone...sorry for the wasted forum space. I should have known better. :redface:

(I really dislike most things about getting old.)

Everybody has those days. I will relate a customer story from several years ago.

I have a customer call me because after shutting off his riding mower to talk to a neighbor it wouldn't even crank the engine. He even had the neighbor attempt to start the mower with the same result. So they took the battery out and when to walmart and purchased a new battery, but that didn't help either. At this point he borrowing the neighbor lawn mower trailer, and hooks it behind his van to hauls it the 20 miles to my shop.
'
He pulls in, and without me even unstrapping the mower, I just jump up on it, and pushed the clutch down, bumped the throttle, up and pulled the choke out and immediately started the mower. I then shut it off and restarted another 4 times. At this time the customer gets up on the mower, and pushes the clutch down and starts the mower a couple more times. Which at that time he has discovered the problem the whole time, was he and the neighbor hadn't pushed the pedal down to start the mower.

ILENGINE said:

Everybody has those days. I will relate a customer story from several years ago.

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Ha ha. Thanks. Of course I'd feel better if you as a shop owner had a Homer Simpson moment, rather than you neighbour. But I appreciate the point and feel better.

Thanks again. Cheers.

I wouldn't say I have homer simpson moments very often. What I get are Murphy of Murphy's law moments. And when he shows up, he usually sticks around a week. Those are the weeks that you break more than you fix.

Breaking center ring of a new piston ring assembly and having to order a new ring set, from the manufacturer since it was a new style aftermarket piston ring assembly that hadn't hit the supplier chain yet. cost of rings $65

Installing a set of new rings on an other atv, that the bottom ring of the oil control ring dislodged from the piston and got caught between the piston and the new replacement cylinder. causing a nice gouge mark down the side of the cylinder. Cost of another replacement cylinder and rings $400.

Striking a wrench with an open hand to create a impact effect to loosen a stubborn bolt that resulted in me tearing a tendon in my left shoulder. recovery time 5.5 months.

And my favorite, ordered a replacement ignition module that had been available for $68 for a customers $299 chainsaw, and when the module arrived discovered that they had marked the cost of the module up to $248

ILENGINE said:

I wouldn't say I have homer simpson moments very often. What I get are Murphy of Murphy's law moments. And when he shows up, he usually sticks around a week. Those are the weeks that you break more than you fix.

Breaking center ring of a new piston ring assembly and having to order a new ring set, from the manufacturer since it was a new style aftermarket piston ring assembly that hadn't hit the supplier chain yet. cost of rings $65

Installing a set of new rings on an other atv, that the bottom ring of the oil control ring dislodged from the piston and got caught between the piston and the new replacement cylinder. causing a nice gouge mark down the side of the cylinder. Cost of another replacement cylinder and rings $400.

Striking a wrench with an open hand to create a impact effect to loosen a stubborn bolt that resulted in me tearing a tendon in my left shoulder. recovery time 5.5 months.

And my favorite, ordered a replacement ignition module that had been available for $68 for a customers $299 chainsaw, and when the module arrived discovered that they had marked the cost of the module up to $248

Click to expand...

OMG. OK, thanks. Now I feel better. Or at least better than the time I found the carb gasket for an MTD snowblower I had been looking for for two hours in the bottom of my coffee cup.

Cheers. I appreciate your experience and humor.