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Discussion Starter #1
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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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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Discussion Starter #5
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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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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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?
 

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Discussion Starter #9
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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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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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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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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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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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.
 

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Discussion Starter #16
MORE SPECIFIC INFO



I took off some of the tin and was able to clear a lot of gunk from the rear fins. Made a huge difference- now i have lots of air blowing out the front, more on the right than the left but the exhaust on the right still gets insanely hot.

Like after after less than a minute you can't hold your hand an inch away. The left side seems to heat up normally.

The head itself on the right did not seem to get that hot.

So does that point to a bad exhaust valve?

thanks
 

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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.

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.

I picked up a Troy Bilt GTX20 last year with the "shrouded" Kohler. I was going to remove the shrouds thinking that I'm not running it during the winter, there is no sense in keeping all that heat trapped in there. Why would the shroud be required ???
 

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The shrouds create sort of a wind tunnel keeping the air around the fins moving and cooling the engine...that is why it is important to clean out under the shrouds...they become clogged with grass and seem to be a favorite nesting spot for mice....I picked up a John Deere one time and the mice had used almost a whole blanlet to make a nest..it was jam packed tight under the shrouds...I had to pick it out with an o ring hook
 

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Discussion Starter #19
Yeah, i totally get the shrouds. It's like the tin on the aircooled VWs (yes, I'm that old)

But the rapid heating has to do with something wrong in the engine i'm thinking valve, just trying to figure out the path forward ?
 
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