Kohler 25 hp problem????

shelbygtFebruary 21, 2007

I have a Kohler 25 hp two cyliner motor. I noticed that the left cylinder sparkplug always seems to burn rich which a layer of sooty black deposit on it. The right cylinder sparkplug appears to burn normal. I may get a just an instant puff of black smoke on start up, but I figured that was due to the choke. Otherwise no smoke at all.

Funny thing is, this is my second 25 hp Kohler and my first one did the exact same thing. Guy at my repair shop says this is normal and typical of small two cylinder engines. Claims he sees it with Kawasaki, Kohler, Honda, etc.

Does this seem right? Can anyone out there relate similar experiences?

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I do know that one Automobile engines there is often one cylinder that (depending on the engine) consistently fouls more than the others.

Personally, if you are getting good power and are not consuming excess oil I wouldn't worry about it.

Just MHO

Good Luck

    Bookmark   February 21, 2007 at 2:13PM
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Twin cylinder engines that run single-barrel carburetors/intakes will often burn slightly richer on one cylinder. I believe Kohler runs single-barrel carbs on that model. I does happen on other makes of twins, even Harleys.

    Bookmark   February 21, 2007 at 2:13PM
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Keep an eye on your oil consumption and if one of the plugs starts to foul........you need head gaskets. Head gaskets are a common replacement on newer Kohlers, then they are fine.


    Bookmark   February 21, 2007 at 8:38PM
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Been there done that with the head gasket thing, Georg. Actually that is part of the reason why this is my second motor. The first had so many problems starting at 11 hrs with the head gaskets, that I finally insisted on an entirely new motor. The new motor has the new design heads and uses nuts and studs to secure the heads to the block vs the old method of thru bolts. She runs great and no more problems after 150+ hours. My concern is just with the left cylinder burning richer. Plugs are not fouled with oil.

    Bookmark   February 22, 2007 at 9:00PM
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Whether a Kohler Engine has studs/nuts or bolts does not indicate it is a new design. New engines even today are built with bolts. It is just a preference that is set up when an engine build is created.

IMO, nuts/studs always hold better than bolts.

Kohler did make some changes to prevent head gasket failures. What is the serial number of your engine?

Also, make sure you run your engine at full throttle - this is the way these small air-cooled engines are designed. 93 octane fuel wouldn't hurt either.

    Bookmark   February 23, 2007 at 5:30PM
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I have an 18hp Kawasaki Air Cooled twin in my JD 325. The left spark plug always ends up darker than the right. The left cylinder is also lower than the right, making it closer to the oil sump. I have checked the compression, and they are the same, or at least within 2 PSI. The dealer told me that was normal in the twin engines. He seemed to think it was caused by the carburation path. Whenever I removed the plugs to clean them, I would swap sides after cleaning them. However, sparks plugs are cheap. It is probably better to just replace them.

    Bookmark   February 23, 2007 at 7:59PM
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Crankshaft, during the off season I do tend to putt around at half throttle as I am not cutting grass. Using 89 octane fuel. Kohler did assure me that my new engine does use the redesigned parts. They pointed out that part of the headgasket fix was the use of studs/nuts vs. bolts.

Cranheim, your observation with your Kawa confirms what my service guy said about seeing this condition in other small 2 cylinder engines.

This condition has been there since the engine was new and it runs fine so I guess I just won't worry about it.

Thanks to everyone for their replies.

    Bookmark   February 23, 2007 at 9:53PM
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I too have a 25 hp Kohler in my Craftsman Lawn Tractor and it is using oil (about 1 qt in 2 hours). I bought the tractor new about 4 years ago, is this one of these poorly designed versions? It seemed to start burning oil all of the sudden, but it runs great and I have always maintained it properly. Is it likely a failed head gasket? What fails on the head gaskets to cause it to burn so much oil?

    Bookmark   May 29, 2007 at 11:20AM
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I have a CH740 Kohler engine on a Z-turn mower.
Model: CH740
Serial: 3224004451
Year: 2002
Spec: ***** - 0007
Major oil consumption!! Tore it down, compression was fine. Head gaskets were shot. Leveled the heads and new gaskets BUT the left cylinder still is fouling out plugs left and right!! Where is the oil coming from?? How is it getting up to the chamber?? Any hints or inherant problems?? HELP!!!

    Bookmark   July 2, 2010 at 9:49AM
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I'm also in Ohio and having the exact same situation with my Kohler Command CH25 on a Z-turn. Head gaskets replaced. Heads replaced. New breather kit. Even a new exhaust valve. LEFT PLUG IS STILL FOULING after about 2 to 2.5 hours of running under load (and consumes about .75 quarts of oil in that amount of time). No fouling occurs when engine runs for hours in the shop with no load. Any solutions would be great. I too want to know where the oil is coming from. We else would it be if it tests fine on bench test but then chugs oil when it's under load. Rings? Cylinder walls? Anyone? Thanks...

    Bookmark   August 16, 2010 at 10:20PM
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1 quart in 2 hours? How does this compare to a commercial mosquito fogger?

    Bookmark   August 17, 2010 at 5:14AM
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i got a big oil use issue with a Kohler twin SP27 using a lot of oil and fowled plug on the the oil cap side of the engine. FYI, i read somewhere on the net to check the reed valve- whatever that is- a busted or defective one leads to excessive oil use apparently. Anyway, my low oil pressure light was not working from the start, and i ran mine with low or no oil - real smart i am. Now, i am looking for a short block to get me going again. the thing runs but uses an unsustainable amount of oil because the oil rings on the piston and bore are probably damaged - i think. As i have to add oil again after a couple of hours hard running, and even one cylinder stopped firing because of the oil on the plug. I think the compression and oil rings are gone, and it would have been due to running it on a hot day/week with low oil, from what i am recollecting about the machine usage and engine noises. the machine was showing 20% pressure loss on one side, after only 200 hours. Another veteran mechanic said that all air cooled engines all use some oil as a part of normal running, and that it is important to keep an eye on your oil levels at all times, or you will get what i got. The mower repair guys said i 'dusted' the engine by not maintaining clean air filters, but i am pretty certain i damaged the engine rings and bore because of low or no oil. i am going to order a new engine from the USA , and have the old one rebuilt in a engineering shop that specializes in cylinder sleeves and pistons. Its an expensive pain in the rear but, having a spare good engine block ready to go is the only way i can think of to control the engine reliability situation long term .

    Bookmark   April 17, 2012 at 12:19PM
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***"having a spare good engine block ready to go is the only way i can think of to control the engine reliability"***
That is funny. Most of us here always thought the way to control engine reliability was to keep close tabs on things like oil levels and regular oil changes.
Boy, I learn something new every day :^)

    Bookmark   April 17, 2012 at 1:26PM
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You can always tell when someone has just registered when 2 year old threads start popping up!

    Bookmark   April 17, 2012 at 4:11PM
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i have a CH25 that had only one cylinder working. Replace the head and it runs well for about 30 minutes under load and then starts popping and losing power. Plugs are burning fine, fuel is good. The leak down has not changed since replacing the head and both are good. Anyone experience this problem before or any ideas. My mechanic is stumped.

    Bookmark   June 9, 2014 at 7:55PM
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Clogged atmospheric vent hole in fuel filler cap. Probe vent hole with a stiff wire (think paperclip) and blow out with compressed air, with the cap removed from the tank, of course.

    Bookmark   June 10, 2014 at 12:24AM
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