Kohler M12 won't go over an idle

[VegetiveSteam]

I do have a good spark but replaced the plug just to be sure. So, it starts, will only run at an idle for a few seconds and dies. Start, run, repeat.

Not trying to offend here so hope you don't mind me asking, how do you know it has good spark? What was your testing method?

 

[VegetiveSteam]

I checked and I have great fuel pressure and volume, I pulled and cleaned the carb, no help. I replaced the carb for the one on my other running mower, and even used a remote, gravity fed fuel tank just to be sure.

How about the fuel itself? You've eliminated the carb and fuel delivery as being an issue by trying another carb and gravity feeding fuel (assuming to the carb?) but was this all done with the same fuel?

 

[peejo50]

Take some starting spray. Shoot some into the carb when it dies. See if it will run on carb like spray.

Tried that with no results.

 

[peejo50]

How about the fuel itself? You've eliminated the carb and fuel delivery as being an issue by trying another carb and gravity feeding fuel (assuming to the carb?) but was this all done with the same fuel?

No, I had fresh fuel.

 

[peejo50]

Not trying to offend here so hope you don't mind me asking, how do you know it has good spark? What was your testing method?

I set the plug on top of the engine and could see a strong visible spark. I also have a passive tester that shows ignition for the short time it's running. for

 

[slomo]

I set the plug on top of the engine and could see a strong visible spark. I also have a passive tester that shows ignition for the short time it's running. for

One of those inline Christmas lights does not load test the coil. Only indicates spark at that time. All electrical circuits require testing under load.

So you have air, fuel and spark. Only thing left is compression. What do you have for compression?

 

[VegetiveSteam]

I set the plug on top of the engine and could see a strong visible spark. I also have a passive tester that shows ignition for the short time it's running. for

Is your tester something like one of these?

 

[peejo50]

Is your tester something like one of these?View attachment 65647View attachment 65648

The engine has a compression relief so it will only show a rate of about 35 lbs., and I don't have access to a pressure tester. The spark tester looks more like a short pen with a light in a window and a metal cap. Something I've been using for 50 years or so. Also, this has a magneto for ignition, and I will need to find the specs on it to check. I got a reply on another forum from a guy that raced sprint cars. He said he had some strange experiences dealing with the magnetos in them and this sounded like one of them. Since I've tried a different carburetor, a different fuel source and even starter fluid, plus the fact that it does start and run, I'm ruling out fuel, valves and timing and going with an ignition issue.

 

[VegetiveSteam]

The engine has a compression relief so it will only show a rate of about 35 lbs., and I don't have access to a pressure tester. The spark tester looks more like a short pen with a light in a window and a metal cap. Something I've been using for 50 years or so. Also, this has a magneto for ignition, and I will need to find the specs on it to check. I got a reply on another forum from a guy that raced sprint cars. He said he had some strange experiences dealing with the magnetos in them and this sounded like one of them. Since I've tried a different carburetor, a different fuel source and even starter fluid, plus the fact that it does start and run, I'm ruling out fuel, valves and timing and going with an ignition issue.

That's why I was asking about the ignition testing method to try and rule that out. Did you actually test compression and get 35 psi because even with a compression release 35 psi would be extremely low. 70 psi would be more reasonable but a leak down test is the best way to check and engine with a compression release. On an engine without a compression release you'd typically be looking at 150 psi or higher.

Good luck and if you need a manual, you can get it a Kohlerengines.com. Go to Service & Parts. When you get to the manuals page simply type in M12 in the model number field, scroll down and you will find a service manual.

 

[slomo]

This is what you need.