Me thinks you need a new Ignition coil.
Kohler Command 12.5hp Spark Issue
I have a Cub Cadet HDS 2135 (about 20 years old) with a Kohler Command 12.5HP OHV engine in it. The other day, while mowing, it died, suddenly. It didn't sputter to a stop, but just died, as if you turned the key off.
After messing with it, I believe the spark is very weak, and I don't know what to do at this point.
A month or so ago, the engine wouldn't start, and I traced it down to a faulty spark plug. The plug wouldn't fire, at all. I put an old plug from a 350 on the wire, and it sparked, so I bought a new spark plug for the Kohler and everything was fine. A month later (now), same problem. No spark, whatsoever, on the plug. Put a plug out of my truck on it, and it fired. So I bought a couple extra spark plugs, just in case. Besides the spark plug going bad (which I have never seen before, either), here's where it gets weird.
I gapped the new plug to .040. I stuck it in the wire, and clamped my jumper cable from battery negative to the plug. It fired. So I put it in the engine, and it wouldn't fire. So I took it back out, put the clamp back on it, and no spark. Hmmmm.
I thought maybe safety switches were the cause, I checked the negative kill wire that goes up to the magneto, but no ground, so it should be okay. I unplugged that wire off the magneto just to be sure. I checked the oil pressure switch, but it made no difference. I left it disconnected. I thought maybe the engine ground was bad (even though the starter runs great), so I took my jumper cables and jumped the negative battery terminal to the engine block.
At this point, there's not much to the ignition system. There's a magneto, the spark plug wire and a kill wire. That's about it. I thought maybe something was up with the magneto, so I took my induction timing light that I use on my truck (the kind that clamps around the plug wire) and cranked it. Strangely, the pulse was intermittent. It would flash a few times, then stop. Should a timing light that is used on a truck still work on a small engine??
I put yet another spark plug in it. When I look at the spark, it seems very weak. Maybe I'm used to what spark looks like on a 350 and not a small engine, but to me, it seems very faint. Right now, I can get it to spark while cranking, but only here or there. Not enough to get it started, but enough to tell that it's sparking.
I'm pretty positive the issue is in the ignition system somewhere. Wiring is okay. I cleaned the carb just for shits and giggles. It's getting gas. Ether won't make it fire, or even change how it sounds when cranking. Battery is good, and most of the time it was starting, the battery was attached to a charger/starter. The only thing that I can even think could still be the issue is if there is some kind of coil in the magneto that has gone bad. I don't have much experience with magnetos, so I really don't know if there is even a coil.
Any suggestions would be greatly appreciated, because I'm about out of ideas.
Thanks
Greg
After messing with it, I believe the spark is very weak, and I don't know what to do at this point.
A month or so ago, the engine wouldn't start, and I traced it down to a faulty spark plug. The plug wouldn't fire, at all. I put an old plug from a 350 on the wire, and it sparked, so I bought a new spark plug for the Kohler and everything was fine. A month later (now), same problem. No spark, whatsoever, on the plug. Put a plug out of my truck on it, and it fired. So I bought a couple extra spark plugs, just in case. Besides the spark plug going bad (which I have never seen before, either), here's where it gets weird.
I gapped the new plug to .040. I stuck it in the wire, and clamped my jumper cable from battery negative to the plug. It fired. So I put it in the engine, and it wouldn't fire. So I took it back out, put the clamp back on it, and no spark. Hmmmm.
I thought maybe safety switches were the cause, I checked the negative kill wire that goes up to the magneto, but no ground, so it should be okay. I unplugged that wire off the magneto just to be sure. I checked the oil pressure switch, but it made no difference. I left it disconnected. I thought maybe the engine ground was bad (even though the starter runs great), so I took my jumper cables and jumped the negative battery terminal to the engine block.
At this point, there's not much to the ignition system. There's a magneto, the spark plug wire and a kill wire. That's about it. I thought maybe something was up with the magneto, so I took my induction timing light that I use on my truck (the kind that clamps around the plug wire) and cranked it. Strangely, the pulse was intermittent. It would flash a few times, then stop. Should a timing light that is used on a truck still work on a small engine??
I put yet another spark plug in it. When I look at the spark, it seems very weak. Maybe I'm used to what spark looks like on a 350 and not a small engine, but to me, it seems very faint. Right now, I can get it to spark while cranking, but only here or there. Not enough to get it started, but enough to tell that it's sparking.
I'm pretty positive the issue is in the ignition system somewhere. Wiring is okay. I cleaned the carb just for shits and giggles. It's getting gas. Ether won't make it fire, or even change how it sounds when cranking. Battery is good, and most of the time it was starting, the battery was attached to a charger/starter. The only thing that I can even think could still be the issue is if there is some kind of coil in the magneto that has gone bad. I don't have much experience with magnetos, so I really don't know if there is even a coil.
Any suggestions would be greatly appreciated, because I'm about out of ideas.
Thanks
Greg
1 - 15 of 15 Posts
That was about the only thing I could think of, too. I don't know much about magnetos. The Kohler engine diagram lists an "ignition module", which looks like the stationary part that rides up against the flywheel and has the plug wire coming out of (which I have been referring to as the magneto). Would this be the part?Me thinks you need a new Ignition coil.
That was about the only thing I could think of, too. I don't know much about magnetos. The Kohler engine diagram lists an "ignition module", which looks like the stationary part that rides up against the flywheel and has the plug wire coming out of (which I have been referring to as the magneto). Would this be the part?[/QUOTE
Yes Sir, that is it easy to remove and replace just remove the two mounting bolts, put the new module on, then put a index card under the metal prongs rotate until the magnets grab the index card. tighten the screws and your done. It is also advisable to put a little Loctite on the screw thread prior to re-install to protect against them coming-out under vibration.
Thanks! I'll replace this week and post back what happened!
Replaced the coil and now I have no spark at all.
The first time I thought maybe I had the gap wrong between the magnet and the coil, because I used an index card. So I tore it all back apart and used two feeler gauges between the magnet and coil. Still no spark. Tried two brand new spark plugs (Champion rc12yc gapped to .040) and a known good one out of my truck.
![Auto part Engine]()
The first time I thought maybe I had the gap wrong between the magnet and the coil, because I used an index card. So I tore it all back apart and used two feeler gauges between the magnet and coil. Still no spark. Tried two brand new spark plugs (Champion rc12yc gapped to .040) and a known good one out of my truck.
Did you install the coil upside down on the 2 posts ? It may have an arrow on it showing crankshaft rotation.
Are you sure you have the right coil and the kill wire is NOT grounded out to frame ground somewhere....Replaced the coil and now I have no spark at all.
The first time I thought maybe I had the gap wrong between the magnet and the coil, because I used an index card. So I tore it all back apart and used two feeler gauges between the magnet and coil. Still no spark. Tried two brand new spark plugs (Champion rc12yc gapped to .040) and a known good one out of my truck.
View attachment 1389586
A good system should still spark at .040 . is that the spec? Briggs are gapped at .030. And how are you testing for spark? I just ground an inline tester. No plug. With ground wire off coil to confirm the coil.
I looked at it this morning and compared before/after pics, and it looks like the coil is backwards. I will switch it later and let you know what happens.
I don't have an inline tester (just a regular 12v test light but I don't know if I can use that on a spark plug wire) so I've just been putting a spark plug in the wire, and holding it on a clean bolt head on the block. I also try it on the negative battery post. I also tried using an induction test light (the one I use on my truck) that snaps around the plug wire and pos/neg on the battery.
.040 is spec on that engine.
Thanks for the help.
Greg
I don't have an inline tester (just a regular 12v test light but I don't know if I can use that on a spark plug wire) so I've just been putting a spark plug in the wire, and holding it on a clean bolt head on the block. I also try it on the negative battery post. I also tried using an induction test light (the one I use on my truck) that snaps around the plug wire and pos/neg on the battery.
.040 is spec on that engine.
Thanks for the help.
Greg
You can use a 12v test light, but it likely won't work for more than one cycle before it breaks. The filament uses 12v and you'll be feeding something in the thousands... little amps, but I'd bet the filament goes.
The 'in-line' tester has a male spark plug fitting on one end and a female on the other. The male connects to the plug wire from the magneto, the female conects to the spark plug. Using the tester, you may be able to observe spark going across the tester's gap.
I have had little success using one, so don't ask me.
The faster the flywheel magnets pass by the magneto coils, the higher the output, and the stronger the spark, within limits. All the electricity used to create the spark is generated within some short distance of flywheel & magnet rotation past stationary coils.
If the secondary(plug) coil has broken or shorted windings, it can cause total failure, or if the windings short to each other, limited output. They are 'potted' and the wire coated with insulating lacquer or paint, but over time, heat cycles can cause enough expansion and contraction that the insulation wears off, and cross-connects occur. They can become temperature sensitive in that case, as the contact may come and go with heat. I think you can get total failure or reduced output voltage depending on exactly what happens.
tom
The 'in-line' tester has a male spark plug fitting on one end and a female on the other. The male connects to the plug wire from the magneto, the female conects to the spark plug. Using the tester, you may be able to observe spark going across the tester's gap.
I have had little success using one, so don't ask me.
The faster the flywheel magnets pass by the magneto coils, the higher the output, and the stronger the spark, within limits. All the electricity used to create the spark is generated within some short distance of flywheel & magnet rotation past stationary coils.
If the secondary(plug) coil has broken or shorted windings, it can cause total failure, or if the windings short to each other, limited output. They are 'potted' and the wire coated with insulating lacquer or paint, but over time, heat cycles can cause enough expansion and contraction that the insulation wears off, and cross-connects occur. They can become temperature sensitive in that case, as the contact may come and go with heat. I think you can get total failure or reduced output voltage depending on exactly what happens.
tom
If you install the coil correctly and gap it with the index card you can chk the spark by grounding the plug to the head or one of the bolts.... you can see a spark in a darken area just by spinning the flywheel by hand (don't get your hand caught in the cooling fins)......
An old burnt out sealed beam headlamp makes a good spark tester--the spark will jump the gap left behind in the bulb's filament when it burns out..
It's easy to see the spark,if it has any,and the risk of being zapped is reduced using one as a tester..
To use it hook the spark plug wire to one of the headlamp's terminals (being careful not to let it ground out against anything)--and run a ground wire from the other terminal,to a good ground..I use an alligator clamp to hook to ground..spin the engine over with the "kill" wire dissconnected,and check for spark..
It's easy to see the spark,if it has any,and the risk of being zapped is reduced using one as a tester..
To use it hook the spark plug wire to one of the headlamp's terminals (being careful not to let it ground out against anything)--and run a ground wire from the other terminal,to a good ground..I use an alligator clamp to hook to ground..spin the engine over with the "kill" wire dissconnected,and check for spark..
the electronic magneto needs higher rpm than the points setup to produce a spark. Not likely that hand turning will reach that rpm. I think it's about 500rpm.If you install the coil correctly and gap it with the index card you can chk the spark by grounding the plug to the head or one of the bolts.... you can see a spark in a darken area just by spinning the flywheel by hand (don't get your hand caught in the cooling fins)......
Good news! The coil was on backwards. I swapped it last night and now it fires up faster than it ever has! I can't believe I didn't catch that...
Thanks again for all the help!
Greg
Thanks again for all the help!
Greg
1 - 15 of 15 Posts
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