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post #1 of 35 Old 08-25-2019, 03:46 PM Thread Starter
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Kohler 20 mystery

I acquired a Simplicity Sunstar 20 project. History unknown.

It starts easy and runs well.

Then it gets weird.

The right cylinder get hot way faster than the left. within a few minutes you can't hold your hand an inch from the right side of the muffler.

Airflow coming through from the back seems about the same on both sides.

Then when i shut it down it keeps running. I thought it was dieseling from the overheating but it's too smooth.

I pulled the left plug wire and it's still running then i pull the right and it shuts off.

So, it's still getting spark, the key switch is a mess that's not a surprise.

Could there be any connection between both issues, the overheat and the not shutting off?
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post #2 of 35 Old 08-25-2019, 03:49 PM
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Re: Kohler 20 mystery

You're sure the left side is really running?

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post #3 of 35 Old 08-25-2019, 04:39 PM Thread Starter
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Re: Kohler 20 mystery

Quote:
Originally Posted by kklowell View Post
You're sure the left side is really running?
Good question, Yes, i confirmed both cylinders are firing when it's running
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post #4 of 35 Old 08-25-2019, 06:07 PM
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Re: Kohler 20 mystery

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Originally Posted by hertfordnc View Post
Good question, Yes, i confirmed both cylinders are firing when it's running
How did you do that? I've had issues with a tecumseh vtwin. I have used laser temperature gauge on exhaust pipes . other method I use is an inline spark tester on both cylinders. They have exposed metal so I can ground spark out with alligator clip jumper. My left wasn't running. When I grounded it there was no change in running. If I grounded right then engine stopped. Once it was fixed then grounding either one resulted in a small drop in rpm.
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post #5 of 35 Old 08-25-2019, 06:30 PM Thread Starter
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Re: Kohler 20 mystery

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How did you do that? .
Methodically; while running i pulled each wire, in both cases it continued to run on one cylinder.

Until i shut the key off at which time it would continiue running after i pulled the left wire but shut off when i puled the right wire.
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post #6 of 35 Old 08-25-2019, 07:15 PM
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Re: Kohler 20 mystery

Okay.. so there's spark on both sides. How about compression?


As far as the continued running, you say the key switch is a mess. That's probably the problem, there. I doubt it would be associated with the left/right cylinder issue.

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post #7 of 35 Old 08-25-2019, 07:25 PM Thread Starter
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Re: Kohler 20 mystery

I haven't measured the compression but it seems to run great. lots of power.
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post #8 of 35 Old 08-25-2019, 07:39 PM
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Re: Kohler 20 mystery

I'm just running down the list... For an engine to run (in this case one cylinder of an engine) you need spark, compression, and fuel...

Those do all have to happen in a reasonably proper timing, but right side timing seems correct so I would deal with timing, if need be, later.


I've heard these things run fine on one cylinder...


By the way, which model Kohler engine?

Late 50's Bready... aka, "The WoodRat"

1969 John Deere 110 w/front blade

1998-99 MTD/AYP "Black Thing" 18hp Briggs MUTT-Mower

2002 Cub Cadet 2166 (in process)

2006 Cub Cadet GT2544

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post #9 of 35 Old 08-25-2019, 08:07 PM Thread Starter
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Re: Kohler 20 mystery

It's the CH20S.

Yes, it does run remarkably smooth on one cylinder but much better on two.

So, probably no connection between the heat and the continued ignition. I'll figure out the electrical issue.

The heat is a problem. What are the most likely causes?

I have not completely ruled out obstruction on the fan side of the cylinder.
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post #10 of 35 Old 08-25-2019, 08:27 PM
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Re: Kohler 20 mystery

The fins can get packed with grass/dirt/etc. over time. You have to take the sheet metal shrouds off to clean them out. Don't run the engine without them though.


You don't need a compression gauge for a quick test. Just pull the plugs with the engine cold and see that you have air forcing out of the spark plug holes... Pretty quick and easy to check. Sometimes valve seats come loose and leak compression, or hold the valve open. Not a definitive "test" but would clue you into whether it has any at all or one much more than the other.

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post #11 of 35 Old 08-25-2019, 08:32 PM Thread Starter
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Re: Kohler 20 mystery

I did the finger compression test- seemed good and uniform.

I'll pull the covers next.
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post #12 of 35 Old 08-25-2019, 10:29 PM
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Re: Kohler 20 mystery

So it stays running with key off. You pull left wire and it stays running. Then pull right wire and it stops. I would check the kill wire circuit on the right . maybe it's circuit is open somewhere on the way to the keyswitch.
When it stays running when left is off do you replace it before removing right? If both are off it can't possibly run. So what if you pull right off first? Does it stop? If yes then left kill circuit is good. If it only stops with both wires off then likely it's in the kill circuit after coil kill wires join or the keyswitch or wiring from it to ground.
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post #13 of 35 Old 08-25-2019, 11:38 PM
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Re: Kohler 20 mystery

Always pull the shroud. I find BRICKS of grass and nests in these all the time. One side will be almost perfect and other massively blocked.
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post #14 of 35 Old 08-28-2019, 01:18 PM
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Re: Kohler 20 mystery

You likely have a leaky exhaust valve on the hot side. The valve is glowing red causing the run on when shutting down. I would invest in a compression tester and check it both cold and hot. Common problem, especially if the cooling fins on the heads are clogged with dirt/garbage preventing transfer of heat to the air. You will need to machine grind the valves (or buy new ones) and at least carbide grind the seats. Lapping will only make it worse. Pull the heads and compare one side to the other, hot exhaust valves usually have white carbon on them. Good Luck.

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post #15 of 35 Old 08-28-2019, 02:36 PM
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Re: Kohler 20 mystery

Also check for any intake leaks. This could cause the right cylinder to run lean, causing the overheating. Easiest way to test is to carefully spray starting fluid around the right side intake. If the engine speeds up you have a leak.

I give advice for free. Just remember though, you get what you pay for.
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