Kohler CH25 with fixed timing ignition: what aftermarket coils will work with this setup?

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  • / Kohler CH25 with fixed timing ignition: what aftermarket coils will work with this setup?
Hi all. New to forum. But reading some of the threads here, I think I've finally come to the right place for some answers about fixed ignition coils.

I have an old (as in 2000ish vintage) Yazoo Kees ZTR with a Kohler CH25 V twin engine with a fixed timing ignition system, i.e., no SAM.

I bought it a while back from a mower repair guy outside Waco (I'm in Austin, about 100 miles away, saw it on side of road while driving back from Dallas, bought it on a lark). Repair guy had modified it with a push button starter after the ignition switch starter mode failed (though "on" position still works to power the harness), so wiring harness has been modified (the oil sentry oil pressure sensor on the breather has also apparently been disabled/bypassed as well but not the oil level sensor).

The tanks totally clogged up, but have since rebuilt the entire fuel delivery system. New tires all around as well. Replaced the main seal and rebuilt the breather (as I was thinking the main seal oil leak was caused by pressure blow from a broken breather reed). So I am vested in the ZTR now.

It's served me well for almost a year.

Cranked it up after sitting the winter to cut an acre property I have. It ran a bit warming up (with help from some starter fluid to get it going), then it suddenly stopped running, so checked the three things an ICE needs: compression, fuel, spark.

Compression and fuel are good, but spark appears inconsistent: weak to non-existent, both using a tester (automotive -- the HFT in-line spark type with a very faint orange light) and directly thru the grounded plug (sometimes a spark, sometimes not).

I want to replace the coils first and see if that is the issue, but apparently Kohler doesn't offer the simple single blade coils for the fixed ignition system on the CH25 anymore: instead, Kohler makes an ASAM/MD (something speed something module / magneto discharge?) retrofit kit (24-755-308-S) that includes new 2 blade coils, some new harness wiring and a new flywheel/magneto -- and is priced accordingly, i.e., expensive.

I am not too motivated to go retrokit and replace the flywheel (yet), so I would like to see if I can find some aftermarket coils that are compatible (even if they requires modification like rewiring or an additional resistor in-line) with the CH25 fixed ignition setup.

I've read about some aftermarket coils that work with some modification -- two specifically, one suggests adding a 4K ohm resistor in-line to get the coil resistance up-to-spec, and another suggests just disconnecting the kill ground wire to the coil altogether and just letting the carb fuel cutoff shut down the engine.

I'm looking for anyone who has the same system and has found some coils that will work -- even with some modification.

Thanks in advance for any help you might be able to provide me.
 
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ILENGINE

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  • / Kohler CH25 with fixed timing ignition: what aftermarket coils will work with this setup?
Lets start with the model and spec number from the engine. Can be hard to read on Kohler sometimes so may have to get creative. Then we can decide what your options are.
 

Hammermechanicman

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  • / Kohler CH25 with fixed timing ignition: what aftermarket coils will work with this setup?
There a couple different ignition systems Kohler used on the CH engines. Do you have the engine numbers? If it is a DASI system you can get a kit to replace the coils with MDI ones that are just standard coils. Regular Kohler coils won't work. 32 707 01 s is the kit number if you are replacing a DASI system. If it is an ASAM system then the kit with a flywheel.
 
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  • / Kohler CH25 with fixed timing ignition: what aftermarket coils will work with this setup?
Thanks for the reply.

There are no tags/numbers I can find ANYWHERE on the engine: remember, it may be as much as 20 years old, so if it was on a tag, then it is likely long gone (though the stamped metal Yazoo Kees model and serial number tag is still riveted to the chassis near the engine -- see attached photo).

From the service manuals -- and the fact the coils have a single blade connector and there is no SAM. The diagram calls it a
Capacitive Discharge (Fixed Timing) Ignition System. Is that the same as a DASI?

BTW, I found these aftermarket single blade coils that claim they are compatible with the CH25. Do you think these will work?


Interestingly, on the coil I pulled out of the cowl (brand INEL? part no. 32 584 01), the coil pickup/sensor is corroded and completely flush with the coil body, while on all the versions I have looked at online, the pickup extends a bit (1-3mm?) from the plastic body of the coil.

Picture1.gif

Coil Pack.gif
 
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  • / Kohler CH25 with fixed timing ignition: what aftermarket coils will work with this setup?
OK, now that's good news. Thank you so much for that old part, new part cross-reference.

I actually read the reviews on this eBay listing before posting this thread, and they were actually quite useful/insightful. It's where I got the idea/insight about the internal resistance issue with these vis-a-vis the discontinued 32 584 01 coil and ways to work around it (by either just disconnecting the kill wire/blade or by putting a 4K ohm resistor in series to get the resistance up to where it needs to be -- did you see any other solutions suggested in the reviews?).
 

StarTech

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  • / Kohler CH25 with fixed timing ignition: what aftermarket coils will work with this setup?
I never heard of doing that as the Kohler coils have internal steering diodes and don't need such an added part. Even the Briggs coils only need a pair external steering diodes to prevent them from interfering with each other. Must be a poor design if it needs to be done.
 

bertsmobile1

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  • / Kohler CH25 with fixed timing ignition: what aftermarket coils will work with this setup?
Thanks for the reply.

There are no tags/numbers I can find ANYWHERE on the engine: remember, it may be as much as 20 years old, so if it was on a tag, then it is likely long gone (though the stamped metal Yazoo Kees model and serial number tag is still riveted to the chassis near the engine -- see attached photo).

From the service manuals -- and the fact the coils have a single blade connector and there is no SAM. The diagram calls it a
Capacitive Discharge (Fixed Timing) Ignition System. Is that the same as a DASI?

BTW, I found these aftermarket single blade coils that claim they are compatible with the CH25. Do you think these will work?


Interestingly, on the coil I pulled out of the cowl (brand INEL? part no. 32 584 01), the coil pickup/sensor is corroded and completely flush with the coil body, while on all the versions I have looked at online, the pickup extends a bit (1-3mm?) from the plastic body of the coil.



View attachment 51159
That is not corrosion it is a different design
When the high silicon transformer steel core rusts it starts between the laminations causing them to fan out .
This is just an older design where the need to save money was not so great.
Rust on coils is not a problem unless it gets so thick that the core contacts the magnet as it passes .
The steel used will rust sitting on your workbench while you watch it .
It is a trade off as to how far the legs extend past the actual coil.
Too close and you get insufficient cooling
Too far away and you reduce the intensity of the magnetic flux that the coil windings are exposed to.
That particular set up looks like it is a rebuildable one . Many of the early ones the laminations & the coil were 2 distinct pieces so you just swapped the coil section when they went bad
In fact they were a 3 part system as trigger chip was a standalone part .
 

bertsmobile1

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  • / Kohler CH25 with fixed timing ignition: what aftermarket coils will work with this setup?
I never heard of doing that as the Kohler coils have internal steering diodes and don't need such an added part. Even the Briggs coils only need a pair external steering diodes to prevent them from interfering with each other. Must be a poor design if it needs to be done.
As the reviews say it works fine as a single it is most likely from a different engine and just happens to work with Kohlers .
Briggs are trying to force all the old Power Torq engines to be scrapped. They did it by upping the price of the magneto coils to $ 180 wholesale a price no one will pay for a push mower coil
Thus the search for an alternative supply by downloading catalogues form the factories, there are a lot more of them than I though so it is back to pirating old mowers
 
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  • / Kohler CH25 with fixed timing ignition: what aftermarket coils will work with this setup?
I am guessing that Kohler is doing the same as Brigs, i.e., forcing obsolescence, by discontinuing the 32 584 01 coil for a fixed timing system and in its place offering their (expensive and intensive-to-install) retro kit if you want to stay correct.

I am going to try the other coil recommended in this thread and will report back.

BTW, I ohm'ed the coil I pulled off (in the pic) and it measures infinite/open between the kill switch blade and ground (the metal attaching body of the coil) and between the spark plug boot connector and ground. Though the Kohler CH25 service manuals (I have two different ones; it appears one is for the DIYer (80ish pages, 3.5mb) and the other for a repair shop (200ish pages, 6.5mb)) do not provide a specific resistance tests/specs for the single blade/fixed timing coil (only tests and specs the 2 blade smart spark coils), I think that the measurements I did do indicate that the coil has failed?
 
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