Riding mower has new plugs, won't spark

Old 05-16-19, 04:34 AM
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Riding mower has new plugs, won't spark

  • Craftsman DYS-4500 riding mower
  • Kohler SV735S-0016 engine
  • easy starter in general
  • recently power is low, but kicks up high for ~2min every ~20min, then back to low power -- almost stalls while cutting due to low power
  • removed plugs, checked for spark by holding against block while cranking -- no spark from either plug
  • replaced plugs, repeated test, no spark
  • voltage between ground and spark plug wire is 12v _at all times_ (how can this be?) -- measured with + lead at plug wire and - lead on block
  • checked fuel lines, seems okay
  • battery voltage 12v+

Suspect: Spark Advance Modules (?) -- but both bad at the same time? Or if one dies, does the other go with it? Or maybe one has been dead for some time and the second just died, and now both are dead? Not sure how to verify.

This video allows you to hear the mower first in "low power" mode, then switching to "normal" for 2 minutes and then back to "low power".

Update: I've preemptively ordered a MDI Ignition Module kit (PN 32 707 01-S) since the SAMs are no longer available for this engine. I hope this does it!
Old 05-16-19, 06:02 AM
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Coil Packs are common failures with Kohler engines but unusual that they would go out at the same time!
Old 05-16-19, 10:00 AM
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I can't tell you precisely what is wrong with your motor but I do know that "no spark" gives you "no power" not "low power". So I have to assume your spark test was incorrect. A proper spark tester would be better to check the condition of your spark.

Other then that, the other possibilities are an intermittent cylinder or a fuel restriction of some sort. Firing on only one cylinder usually results in a smooth reduction to low power. A fuel restriction would probably give more of an erratic change in power.

I would certainly want to get a proper spark test with a proper external spark tester to see how that is.
Old 05-16-19, 11:16 AM
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It may not be the same model, but my neighbor has a Craftsman riding mower that was having low power and sometimes stalling out. It turned out that the gas tank cap was not properly venting. So a small hole was drilled in the top of the cap and it's been running fine ever since.
Old 05-16-19, 04:32 PM
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I agree that the spark test was probably incorrect if your engine will run but you showed no spark. I have never once seen the SAM module go bad on one of these. Not that it can't happen, but it's a pricey part to replace as a shotgun approach.

The 12 volt thing from the coil... are you saying you have 12 volts from the terminal that connects to the spark plug to ground? I can't see how that's possible. With the engine off and the voltmeter set to DC volts, you are getting 12 volts there?
Old 05-16-19, 06:15 PM
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Sorry if I was unclear but the engine will not run/start. The video is from the last time it was running, a few days ago, I went to start it yesterday with no luck. During the last mow session I had turned it off for a break, and it was difficult to re-start. I held the key for maybe 30 seconds and eventually it turned over and I was good to finish mowing, but at reduced power as shown in the video.


I removed the plugs, held the threaded portion to the engine block in multiple areas, held the key on start. The starter motor did its job and I could hear the pistons push air out the spark plug holes, but no spark from either plug.

I will have to re-test the voltage, perhaps I made a mistake -- the results didn't seem right to me either.

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