# Kohler CH 25 Troubles



## 05gmc2500 (May 16, 2007)

I have a Kohler Ch-25 engine on a Zero turn mower . When I first start it when its cold it runs fine. After running it about a half hour it starts to miss and stutter and backfire. I am going to give it a tune up shortly but my suspicion is thats its something else. It runs like a champ for the first half hour and thats it. Some times it works its self out and will run fine again. Dont know if it could be something internal and why only after it is warmed up. Any help would be greatly appreciated. Thanks....


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## 30yearTech (Sep 14, 2006)

You may have a problem with one of your ignition modules breaking down when hot or with the Spark Advance Module (SAM) if your engine is equipped with one. Also check your spark plugs as a fouling plug can cause a similar problem, be sure the plugs are gapped correctly also.


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## 05gmc2500 (May 16, 2007)

I did check the sparkplugs today and found that one was a little fouled out copared to the other side. I will try to run it and see what happens. Thanks for your information. I will keep you updated.


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## ribertgropius (May 22, 2007)

I have some similar problems on my ZTR: my Kohler CH25 backfires and misses (cold or hot), and one of the plugs keeps fouling. Did a compression check on each cylinder and found I have 135 psi on the non-fouling side; 165 psi on the fouling side. Initially, I couldn't understand why the "bad" cylinder was higher, but then reasoned that maybe the higher compression is caused by the oil that is entering the cylinder on that side? The plug on the non-fouling side looked great.

How do you tell if your engine has a SAM or not? Someone else suggested that I may have a head gasket problem, but I would think that would affect compression. Could I have a bad valve seal? Could a plugged breather cause this on just one side? The engine was manufactured in 1994, and has about 900 hours on it. Oil consumption is noticeable, but no blue smoke that I can see.

Thanks.

Robert


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## 30yearTech (Sep 14, 2006)

*www.kohlerplus.com*



ribertgropius said:


> I have some similar problems on my ZTR: my Kohler CH25 backfires and misses (cold or hot), and one of the plugs keeps fouling. Did a compression check on each cylinder and found I have 135 psi on the non-fouling side; 165 psi on the fouling side. Initially, I couldn't understand why the "bad" cylinder was higher, but then reasoned that maybe the higher compression is caused by the oil that is entering the cylinder on that side? The plug on the non-fouling side looked great.
> 
> How do you tell if your engine has a SAM or not? Someone else suggested that I may have a head gasket problem, but I would think that would affect compression. Could I have a bad valve seal? Could a plugged breather cause this on just one side? The engine was manufactured in 1994, and has about 900 hours on it. Oil consumption is noticeable, but no blue smoke that I can see.
> 
> ...


Go to www.kohlerplus.com and login as a guest (must use internet explorer) you can download a service manual for your engine that will give you the test procedures for troubleshooting the ignition system. There will also be illustrations of the SAM so you can see what it looks like and determine if your engine is equipped with one. It will be mounted on the shroud by cylinder and is just a small box with several wires attached to it.


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## ribertgropius (May 22, 2007)

Thanks! I downloaded the manual and was reading through it; they have a pic of the SAM and I will check tonight to see if it is there.


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## ribertgropius (May 22, 2007)

I have a SAM! I will do the leakdown test this weekend and check the timing with a light though I will have to work from the PTO side since the flywheel side is pretty much buried.


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## ribertgropius (May 22, 2007)

*leak down test results*

Finally did the leakdown test today. Did the good side first; could hear just a little bit of air through the dipstick tube, but the gauge did not move at all.

Did the other side (the fouling side; which is the side with the oil fill cap), and could hear and feel alot more air coming out of the dipstick tube. I removed the oil fill cap and could feel the air coming out of that as well. The gauge showed very slight movement but nothing significant in terms of loss. 

So....if I understand correctly what this might mean...and considering the compression is good in both cylinders, with the fouling cylinder actually higher than the non-fouling cylinder, and both over 135...then it appears that I have a head gasket leak on one cylinder, where oil is able to leak into the cylinder, and it is this oil that is fouling the plug and causing the backfiring. I may or may not have another issue with the ignition timing, but there is a noticeable difference in the leakdown test so I think I will start with the head gaskets.

Does this make sense? Thanks.

Robert


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## 30yearTech (Sep 14, 2006)

Yes, I would replace the head gaskets and while you have the heads off check the valves and seats and remove any carbon accumulation.


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## Paladin51 (May 21, 2011)

*CH25 Shuts Off*

Kohler CH 25 on my ZTR loses power suddenly & will shut off if I don't pull back on the steering handles. Attempting to resume forward progress, as soon as the pumps have to build pressure the engine loses RPM/power & will shut off. I shut off the mower deck & return to the shop, leave it set for an hour & it will be good again for 5-10 minutes.

This happened several years ago & I replaced the SAM module. I replaced it again, but this time it doesn't seem to help. I am considering one of the spark modules as it seems heat/electric/electronic related, but am uncertain, doesn't feel right.

Any thoughts?


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