kohler engine igniition unit question

[Mark Leininger]

I have a craftsman lawn tractor with an 18HP Kohler twin, model M18S. Twice now it has failed to start due to no spark. By the time I fiddle with ignition switch and safety switch to see if something is not making contact, it mysteriously starts. I would say in my experience with other small engines the spark intensity looks weak.

My question is about the ignition unit. Does anyone know if these are prone to this type of intermittent failure as they get older (13 years)? Is there some way to diagnose this other than stick a screwdriver in the sparkplug wire to see if there's a visible spark? I hate to drop a bundle on this module if it's not the problem.

If there's a better forum that specializes in small engine repair please let me know, but I saw a fair number of posts on mower engines on these groups. thanks [e-mail]

[Larry]

WHEN there is no spark is the time to T/S. In the meantime, I'd locate a wiring diagram and become familiar with it. OR (when the ignition is working correctly) read it with a meter and draw your own diagram.

Intermitant problems can drive you nuts.

I have device that is used to test the spark on outboard motors that may help. It connects in place of the spark plug and has an adjustable gap for the spark to jump across. Set to a wider gap than the normal spark plug gap, an ignition system will produce a spark to jump the gap (passes the test) or not (fails the test). I don't recall how much wider the 'test gap' will be compared to the spark plug gap. At least it's more accurate (and safer) than the 'screwdriver' spark test.

Larry

[James Sweet]

It's not unheard of for ignition modules or even the magneto coil to become intermittant, problems like that can be real tough to diagnose untill they get worse.

[Larry]

Another thought I'll pass on: Since you suggested 'weak spark', I'd look at the high-tension side of the ignition itself.

Had you said 'strong, intermittent spark', I'd look at the safety switches (neutral, weight on seat, and blade disengage switches) and the primary (low voltage) side of the ignition including battery, connections, ground, etc.

(¯`·._.· £ãrrÿ ·._.·´¯)

[Mark Leininger]

Thanks for all the thoughts. I have the schematic: both the PTO safety and the clutch safety are also in the starter circuit. Since it cranks fine that means it can't be those safety switches. That leaves the seat switch which needs to be open for spark, so I just removed the connector from the switch which guarantees the circuit is open. That leaves only the ignition unit and high tension leads as possible suspects, unless the wire going from the safety switches to the ignition unit is shorted to ground someplace, which would cause the ignition unit to stop funtioning. Not sure exactly what's in this "unit" because there is no coil, points, anything, just this unit. I assume everything is sealed inside so there's not much to debug. There is also a stator called out on the parts diagram, but I haven't dug that far and don't want to.

I don't believe the high tension leads are replaceable. I'm afraid to yank on them hard enough to find out if they come out of the ignition unit. It looks like they were molded in there. I don't want to make the problem worse. The parts diagram does not call them out separately, they are shown as part of the unit. That could just be the big money shakedown.

Thanks to whoever suggested the spark tester. I'm going to look for one of those.

Mark Le> I have a craftsman lawn tractor with an 18HP Kohler twin, model M18S.

[Sam Goldwasser]

First, I'd suggest double checking all wiring connections even if they look secure. Intermittent problems are most often due to things external to the inaccessible innards of the module.

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[Stu MacDonald]

I don't claim to be a mechanic (even though I play one on TV) but it sounds to me like you may have a bad spark plug wire that may be finding ground when you put it back together. Can you leave the cover off and start it then? Try some electricians tape around the length of the plug wire. Also you might want to get some emory cloth and "brighten up" the magneto and flywheel. Sometimes rust can muck things up.

Stu MacDonald

"I think we have more machinery of government than is necessary, too many parasites living on the labour of the industrious." _Thomas Jefferson

[Chas Hurst]

Use an old spark plug and widen the gap to .050 ". Make sure to ground it.

[James Sweet]

You could fabricate one pretty easily, the one I saw was just a plastic ring with a wooden handle on it and some adjustable screws sharpened to a point that formed a gap within the ring. Should be easy to make one out of a short ring of PVC pipe and some screws.

[Not Me]

| | I have device that is used to test the spark on outboard motors that may | help. It connects in place of the spark plug and has an adjustable gap for | the spark to jump across. Set to a wider gap than the normal spark plug gap, | an ignition system will produce a spark to jump the gap (passes the test) or | not (fails the test). I don't recall how much wider the 'test gap' will be | compared to the spark plug gap. At least it's more accurate (and safer) than | the 'screwdriver' spark test.

You can get them at AutoZone for a few bucks. If I remember I'll check when I go by there tomorrow.

[Not Me]

"Stu MacDonald"

| | I don't claim to be a mechanic (even though I play one on TV) but it | sounds to me like you may have a bad spark plug wire that may be | finding ground when you put it back together. Can you leave the cover | off and start it then? Try some electricians tape around the length of | the plug wire. Also you might want to get some emory cloth and | "brighten up" the magneto and flywheel. Sometimes rust can muck things | up.

Had a similar problem with a B&S on a Sear mower. Drove me nuts until my son decided to move the mover after dark. We found the problem to be cracks in the high voltage lead to the plug allowing the spark to 'leak' to ground. (Showed up brilliantly after dark). It was especially a problem on high humidity/wet days.

[Jim Adney]

Of course it's impossible to tell which part is responsible from here, but I would start by making SURE that the ignition switch and all the safety interlocks are okay, as well as all the wiring.

It's easy to blame the active device, but so often the real problem is in the passive parts that we take for granted.

-

----------------------------------------------- Jim Adney [e-mail] Madison, WI 53711 USA

-----------------------------------------------

[Mark Leininger]

Great idea. I'm in the dark most of the time anyhow, so I'll probably be able to see it even during the day.

Not Me wrote:

[Mark C. Mitchell]

My Kohler is in a John Deere/Scotts lawn tractor. I experienced the intermittent problem with the spark last year.

I discovered the lever that engages the mowing action did not return to its correct position. Every now and then when it will not start, just pull the lever back about one inch and see if that is your problem.

Mark Mitchell [e-mail]

[Not Me]

That's a hard way to admit to being a politician.. (ducking and running)

[Chip Stein]

kohler had problems on the magnum 18's at one time. they made a very expensive piece of equipment to test them. they were common to go intermitant. ask a dealer to look up the service bulletin on kohler ignition problems, there is one i just can't remember the number. Chip

[Chip Stein]

kohler had problems on the magnum 18's at one time. they made a very expensive piece of equipment to test them. they were common to go intermitant. ask a dealer to look up the service bulletin on kohler ignition problems, there is one i just can't remember the number. Chip

[Chip Stein]

kohler had problems on the magnum 18's at one time. they made a very expensive piece of equipment to test them. they were common to go intermitant. ask a dealer to look up the service bulletin on kohler ignition problems, there is one i just can't remember the number. Chip

[gothika]

Just take the plug out of the engine, leave it connected to the spark plug lead and ground the tip to the head. Turn the engine over. A good spark is blue/white a bad red/orange. You can often get a weak bad colored spark off of perfectly good coils. This is due to a low or weak battery. Connect a small 2-4 amp trickle charger to the battery during tests to ensure a good spark. There are usually two or more safety switches on riding mowers. One under the seat, one a balance switch that cut engine if the mower tips over. Some will also have a safety on the ejection shute/bag shute. And of course there's the safety pedal. I don't work on many Kohler's but as I recall the engine your talking about is made by B&S. They tend to be a bit particular about coil gap tolerances and proper spark timing(flywheel key must have no twist or shear.)

[Mark Leininger]

Don't think the battery can be involved. This has a magnet on the face of the flywheel that generates the voltage pulse in the primary and an electronic module fires the secondary when it hits its peak. There is no battery connection to the ignition unit.

gothika wrote: