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Kawasaki/John Deere mystery

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Kawasaki/John Deere mystery

Postby BLES » Wed Jul 10, 2019 6:06 pm

John Deere Z717 zero turn with 19hp Kawasaki FH601V.

Starts and runs fine for an hour or so, then starts to misfire, lose power, etc..

Install new plugs. Runs fine for a while, then repeats problem. New plugs always fixes it temporarily. What can cause plugs to go bad?

I suspected heat-related. But, even if machine is left overnight to cool, the problem persists until new plugs are installed. I'm chewing on this mystery until I get home next week, and then neighbor will likely bring it over to me to fix it for him. Hmmmm....

Any thoughts from the experts??

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Re: Kawasaki/John Deere mystery

Postby RoyM » Wed Jul 10, 2019 6:59 pm

Can you install inline spark testers and watch them as the engine falters? If they don't flicker something else is wrong. Also check valve clearances.
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Re: Kawasaki/John Deere mystery

Postby KE4AVB » Wed Jul 10, 2019 7:32 pm

Bles, Have you verify this yourself or is ti base on what the customer is reporting. If just the customer reporting this it might be plugs fouling to a point where they are shorting out. I do know Kawasaki engine like a heavier oil than the Briggs engines. Something like 20w50.
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Re: Kawasaki/John Deere mystery

Postby BLES » Wed Jul 10, 2019 8:42 pm

RoyM wrote:Can you install inline spark testers and watch them as the engine falters? If they don't flicker something else is wrong. Also check valve clearances.


I didn't because the plug wires were too short. But I've also noticed it's hard to "see" a miss sometimes because of the speed they flash.
What else can be wrong that is fixed only by new plugs? Same with valve clearance.... how would that ruin a plug?
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Re: Kawasaki/John Deere mystery

Postby BLES » Wed Jul 10, 2019 8:47 pm

KE4AVB wrote:Bles, Have you verify this yourself or is ti base on what the customer is reporting. If just the customer reporting this it might be plugs fouling to a point where they are shorting out. I do know Kawasaki engine like a heavier oil than the Briggs engines. Something like 20w50.


Neighbor called me today and I ran over as it was missing and loss of power. I only saw/heard it run. Didn't test anything except to check exhaust temps (both sides were the same). He claims the plugs don't look very bad (dirty/fouled) when he changes them. Has been through about 10 sets before he called me.

I will look at it next week likely. He's had it since new (late 90s) and it now has about 1100 hours. Runs nice until the missing starts.

Thanks guys for your ideas.
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Re: Kawasaki/John Deere mystery

Postby bgsengine » Wed Jul 10, 2019 9:29 pm

BLES wrote:
KE4AVB wrote:Bles, Have you verify this yourself or is ti base on what the customer is reporting. If just the customer reporting this it might be plugs fouling to a point where they are shorting out. I do know Kawasaki engine like a heavier oil than the Briggs engines. Something like 20w50.


Neighbor called me today and I ran over as it was missing and loss of power. I only saw/heard it run. Didn't test anything except to check exhaust temps (both sides were the same). He claims the plugs don't look very bad (dirty/fouled) when he changes them. Has been through about 10 sets before he called me.

I will look at it next week likely. He's had it since new (late 90s) and it now has about 1100 hours. Runs nice until the missing starts.

Thanks guys for your ideas.
BLES
I'd suggest starting by doing some homework and make sure exactly which spark plug (BRAND AND Number both!) recommended for it by Kawasaki (Bear in mind different model year engines might need different plugs) and also verify the required plug gap for the engine.. then make sure the new plugs meet all those specs.. If they do then I'd be thinking a marginal ignition system (ever been serviced? maybe too much coil air gap? some rust? loose wiring connections?) but if plugs are not the right ones (They'll probably be wanting NGK and bear in mind that some NGK Specs have no equivalent in Champion or Bosch or Denso.. and vice versa.. ) then you wanna get a couple , and make sure they are gapped to spec, and go from there..

Other things that cause premature fouling (especially the kind that cause dead shorts) - Some fuel additives that may have any metal or carbon to them (builds up on insulator, doesn't burn off, and gives short path to ground that bypasses the plug gap) , Then there's the matter of torquing plugs properly (overtighten them and you can crack the insulator, which obviously allows a dead short to ground) - even adjusting the gap by whacking the electrode on a hard surface (to close gap) or one of those "coin" gappers or screwdriver (prying on center electrode for leverage to open gap) can cause cracked insulators too.. so you wanna use the correct plug gapper tool (metal tang with slot to fit over ground electrode to bend it in or out)..

Of course, there's always the possibility of the changing of plugs being a Red Herring and you may find the plug boots (hardened from heat or cracked, once they collect enough dust from EMF, they start shorting to ground.. and removing them and putting them back is what was "fixing" the problem..) or the plug wire terminal ends (or plug wires) corroded, broken or rusted - again R&R of the plug boots temporarily "fixes" the problem.. In those cases, may need to replace the plug boots and/or terminals.. some of em are just resistor caps (you can thread em on and off the plug wires) while others, might not even be replaceable and require whole ignition coil (unlikely for a Kawasaki, but pretty common on the china clones)
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Re: Kawasaki/John Deere mystery

Postby KE4AVB » Thu Jul 11, 2019 7:29 am

As BGS suggests you got to get your hands on it and do some investigating into the problem. As BGS noted I have seen rusted terminals to cause problems along the other noted items. Not too many auto parts stores carry these terminals either but they can be found which why I have small stock of them here. Just remember that you need the 7mm version and not the 8mm, 9mm, or 10mm versions.
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Re: Kawasaki/John Deere mystery

Postby BLES » Thu Jul 11, 2019 8:13 am

Thanks for the suggestions. Will check it out next week.
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