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TheLawnMowerMan

Kohler M18 troubles

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TheLawnMowerMan

Hello, I recently purchased a Simplicity 17GTH-L from a guy and they had swapped the original 17 horse out for a Kohler M18. He also stated he had just changed the fuel pump before I bought it. I have been going insane trying to get this thing to run right. I've changed the air filter, fuel filter and fuel line, spark plugs, I also readjusted the governor according to the service maunal, and rebuilt the carburetor with no change. What it's doing is at half throttle or more, it's bouncing off the governor, and if I set the idle fuel setting at the recommended setting as the engine manual says it won't start. To get it to start you have to open that setting up real rich and then it idles rough. I pulled the plugs and the second cylinders plug is black from the rich setting but the other plug looks normal. I'm hoping someone can help shed some light on this issue and offer some help. I'd much appreciate any help. Thanks for reading and any help offered.

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ardisam

Any chance, are both cylinders feel hot to the touch? Maybe it through a rod, I had a KT17 do the same thing to me and found one cylinder was cold. Btw, the M18 does not have a coil, they have a magneto.

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TheLawnMowerMan

It is running on both cylinders because I can pull the plug wire on one side and it stays running, then hook that one back up and pull the other and it stays running. The right cylinder misses at idle but runs normal at higher rpm's. I'm pretty stumped on this. Also checked the compression, both have around 80psi. Thanks for the ideas, hopefully if others chime in we can get the problem figured out.

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Dan123

I don't think the carburetor on these engines are set up to be operated with a fuel pump. I was looking in the owners manual and no where did it say anything about it needing a fuel pump or the pressure needed to operate properly.

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TheLawnMowerMan

Well they come equipped with one from the factory. My Kohler K341 16 horse single cylinder also has a fuel pump. I have not seen one without a fuel pump yet. My father has a KT19 in his and it has a fuel pump, my bothers tractor has a M20 and it also has a fuel pump. But it's not a problem of too much fuel due to pressure, the only way it will run is set rich on the carburetor mixture settings. This is a strange problem that has me completely perplexed.

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a_sannine

Could be the springs for the governor not tensioned right , I had that problem one time on my KT17 , the governor kick back .

try adjusting the sensitivity up or down and see if that helps , as far starting could be due to the carb seats damaged .

one more thing to check as well the float ball , not upside down .

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Dan123

If the carb and fuel pump are working ok, then maybe it's a vacuum leak around the intake manifold, cracked manifold or leaking base gasket on the carb. Maybe that would explain the difference in the plugs (rich / normal).

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TheLawnMowerMan

I originally changed the spring tension by switching the holes the spring was on, it helped a bit but still had it hitting off the governor. I have been wondering if there's something wrong with the exhaust valves or possibly the points. I believe it has points, but have no clue where they are on this engine. The other thing I am thinking is the little electronic valve on the carburetor itself, for some reason, as far as I can see now that I've looked at my brothers M20, someone has cut the wire and spliced into it for some reason. Instead of it being wired directly to this resistor, or some kind of switch that's mounted on the cooling fan shroud. I've tried to follow the wires back to where they ran them but it's hard to follow them without taking the dash apart to see where they go and try to figure out why they did that. I am still trying to figure out what that valve on the carburetor is even for. It opens a passage from inside the air cleaner elbow to the float bowl. Anyways I'm going to keep working on the problem until I either fix it. Thanks for all the help so far. If anyone has any other ideas or knowledge of these engines all help is appreciated.

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TheLawnMowerMan

Hmmm. I will have to check the intake manifold tomorrow, and see if there's any noticeable cracks. If not I will replace the gaskets and see what happens. I do know the carburetor to intake gasket isn't leaking as I just replaced it when I rebuilt the carburetor. As far as the fuel pump operation I can only speculate since I was told he just replaced it, and it does appear to be new. But I have had new parts be faulty before. I may buy a new one and see what happens.

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Brettw

The M18 does not have points, it has an electronic ignition module mounted next to the flywheel under the shroud. To me, it sounds like the tension springs may not be quite right, and I would check and reset the governor arm. I had to do it a few times on the M20 before it was correct. Next, even though you did a rebuild on the carb, are you certain all of the orifices and channels are clear? IIRC, on that carb there is a pin hole sized orifice that runs to the idle set screw. Unless you are trying to start the engine with the throttle set at idle, the idle fuel setting should not affect the starting? How about at half throttle with the choke set?

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MikeES

First 80psi compression (if it was done right) is very weak. Kohler recommends at least 90psi. I have a KT17 with 110 psi, and I am strongly considering a rebuild because of excessive blow by.

Second I suggest doing what Brett recommended and completely resetting the governor arm. If that arm is not set right you will drive yourself crazy with trying to adjust the carb. Does your carb have both high speed and low speed jets or is it a fixed high speed jet?

The wire going to the carb is a fuel shut off solenoid. If you think it is causing a problem, pull off the solenoid, pull the pin out from inside the solenoid and reinstall.

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a_sannine

Try this , disconnect the governor arm from the cross shaft , try gently pulling the governor shaft off the engine, if u can then the flapper is broken and that's why it is not adjusting .

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victorsnc

I had a Kohler M18 that developed EXACTLY the same problems you are describing. After trying everything else, I ran a fuel line straight from the fuel tank to the carburetor and PROBLEM SOLVED! In your post you mentioned that the previous owner stated he just replaced the fuel pump. Maybe he got something wrong.

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TheLawnMowerMan

I haven't had any time to do much with it since last post. I did check the intake manifold for leaks or cracks. While it was running I sprayed brake cleaner at the intake ports on both sides and at the base of the carburetor and on the manifold in general. If it had leaks or cracks it should have changed the way it was running either by speeding up or bogging down which it didn't. There was no change at all. I am going to do another compression test on it this week as I don't think I had the throttle open all the way , which would've given a false reading. I am also going to cut the rewire on the shut down control valve on the carburetor and hook it back up the way it was from the factory and check it to make sure it actually is working properly. Anyways thanks for the feedback, and ideas. I will be trying everything, and posting the outcomes afterwards.

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TheLawnMowerMan

Checked the governor shaft to make sure it wasn't broken and that's not the problem. Haven't had much time to check any of the other things I have wanted to due to work wearing me out and life in general getting in the way. Going to spend the weekend going over some other ideas and checking this issue out more, and I will post what I find. Thanks for all the support and ideas, any other ideas are much welcomed and appreciated.

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TheLawnMowerMan

No I actually meant carb cleaner, sorry for the mistake. I'm going to tear the engine down and just go through it. Bought a second GTH-L to push snow while I have this one apart. Not sure when I'll get to this one with my other three projects going on. Will post the rebuild process and tell what I find what the internal issue is.

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