Coil makes a good spark but is bad.

I have 2 coils on a 20 hp kohler command. They are like lawn mower coils, powered by magnets on flywheel. Engine runs just fine. Problem was when I turned the key off, shorting out the coil, only one coil would stop making a spark. So I bought a new coil, replaced the left coil first. Same problem. So I replaced the right coil. Same problem. Now I really out of ideas. I took covers off for the third time and was going to replace both coils with used coils off the 18 hp kohler. I was going to run new grounding wires and connect a ground wire to both coils to make sure coils were properly grounded. Then I discovered when I replaced the right coil, I forgot to connect the kill wire. Here is my sign. Now everything works as it should, finally.

Have you ever heard of a coil making a good spark, but won't stop when shorted out?

george if I had the Kohler part number would be intersting to know what I could get you that coil set up for. Some are amazed at the mark-up on small engine parts e mail open

Thanks Bill, A few months ago I ordered one off ebay, oem kohler $50 shipping included. Then I have 2 used coils off the 18 hp kohler. So I'm good for kohler parts. I will keep you in mind when I need other parts.

So how is the world treating you? As for me, I'm need to invent something to do. Ran out of jobs today fixed tractor and friends wiring job.

Been walking 45-60 minutes a day to fight the battle of the buldge. Not really winning, stale mate.

Have felt better had round with stomack flu bad in hospital 3 days just now getting energy back

Calling them "coils" is a misnomer, they are actually self-contained little solid-state electronic ignition systems.

Also, NOT sure on a Kohler, but on a Briggs there's a diode hidden in the lead to each "coil" to allow them to be shorted/killed for engine shutdown without the two "coils" that fire at different times interacting with each other.

So the key must ground the coil to shut down the engine. I would get a jumper wire to ground out the coils right at the engine to see if there is a problem with the key circuit.

See, you knew what I was talking about. So much for proper terminology on YT. They still have a coil. More like part of a magnetio.

So have you seen anything like it?

Already did that. Had a defective coil.

No, but there's no reason it couldn't happen, since there's a circuit board and electronics "potted" in the "coil".

On the other hand, it would be interesting to put the "bad" original "coil" back in place, making sure the "kill" connection is GOOD and see what happens.

Bob, you want to pay the freight I'll send you the bad coil. Trust me, I tried everything, new kill wire was first thing I did. Then I bought a new coil. Then used a different switch to short out coil. So after taking it apart 3 other times, the last coil substitution worked.

I have a chain saw like that. I had to use the choke to stop it until the choke shaft broke. Then I bought a new saw. I thought it was the switch or wiring too, but I wired a short piece to the coil and a good ground. Put the recoil back on, gave it a pull & it was running.

An ignition module could have the ground tab/stop wire connection fail and still continue to make a spark.

Also, Someone mentioned diodes in the stop wire. On Kawasaki engines, the diode is in the module. If one of the diodes fail in a twin cylinder engine, the other coil will not make a spark. Just an FYI.

A transformer/coil has a given number of turns and an applied voltage across these turns regardless of primary or secondary if a transformer.

The voltage applied is divided by the number of turns making so many volts per turn. This is what drives the current through the coil and makes it work. Magnetic theory says that the transformer will do whatever is necessary to maintain that volt per turn relationship.

If you short a turn or more, like is done with the kill switch, the energy stored in the thing: L di/dt where L is the inductance of it, di is the rate of change of current and dt is the time this occurs, generates the energy stored: 1/2 (Li) exp 2 (squared) which is dissipated in the shorted out coil(s) in an attempt to bring the winding voltage per turn back to where it belongs.

This occurrence prevents development of whatever voltage is necessary to keep the current in all the windings flowing as is the case in a properly working magneto where the voltage rises because the spark plug has not fired and there is no path for current till it does.

So, if you have what you say you have you don't. Laws of magnetics won't allow it. Your ground wire is not grounded.

HTH,
Mark