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

"Mark Leininger" wrote in message
...
I have a craftsman lawn tractor with an 18HP Kohler twin, model M18S.
Twice now it has failed to start due to no spark.

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.


By the time I fiddle
with ignition switch and safety switch to see if something is not making
contact, it mysteriously starts.

Intermitant problems can drive you nuts.



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 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

"Mark Leininger" wrote in message
...
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


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.

"Mark Leininger" wrote in message
...
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.

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 ·._.·´¯)

"Larry" writes:

"Mark Leininger" wrote in message
...
I have a craftsman lawn tractor with an 18HP Kohler twin, model M18S.
Twice now it has failed to start due to no spark.

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.


By the time I fiddle
with ignition switch and safety switch to see if something is not making
contact, it mysteriously starts.

Intermitant problems can drive you nuts.

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 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.

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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On Sun, 11 Jul 2004 13:00:50 -0500, Mark Leininger
wrote:

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


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

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 Leininger wrote:
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

"Mark Leininger" wrote in message
...

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

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

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



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.

"Larry" wrote in message
...
|
snip
|
| 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.

"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.

On Sun, 11 Jul 2004 13:00:50 -0500 Mark Leininger
wrote:

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.

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
Madison, WI 53711 USA
-----------------------------------------------

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:
"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.

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





"Mark Leininger" wrote in message
news
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:
"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.

"Mark Leininger" wrote in message
news | 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.

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