Odd problem with Kohler Command 14HP

Got a mower for someone and was going to be a nice guy and get it all ready to go. Bought it with the engine full of fuel after the needle/seat stuck. Common issue on these. I fixes the fuel system cleaned the carb (done hundreds), etc.

Engine runs with good noises, power, etc BUT has a terrible stumble at low power but goes away with load. This to me point to the pilot circuit in the carb since when on the main jet, it runs fine.

Well, That carb is CLEAN. As I was examining other things trying to spot the issue, I found an obviously blown head gasket that did not show up on comp test but engine would backfire a bit. I figured we had it! Pulling a little air at low power but would level out with load (more throttle). Well, that did not fix it!

I have my inductive light on the coil wire and I just cannot be sure it is missing or not by the light. I removed the kill wire so that is not causing it.

I honestly cannot be 100% sure if this is ignition or fuel related! I did the simple tests to try to prove a fuel issue and makes no difference! Try to add some choke which would usually make a lean circuit happier. No change other than it tries to kill the engine. I removed the air cleaner which will boost the air, no change. No black smoke. I tried tuning the low speed screw. Engine does not seem to care.

What is VERY puzzling is this is LOAD related, not RPM related. If I rev the engine to full throttle, it will stutter around all the way from idle to WOT, but add some load, the engine starts hitting normally.

Very hard for me to consider the coil here but I swear there were a couple times I could not get a hot restart and there was no fire! Actually, in this condition, I had the plug in the boot laying on the engine and I did nothing but walk away to let it cool. Go back and yep... We have fire again...

All this points to the coil BUT add engine load it it starts working??? nah! I starting thinking things like crankshaft play that would cause the airgap to change but I have danced around from .005-.020" on the gap with no change.

Frustrated!!!!!

Did you check the flywheel key?

I had something similar on a Kohler Magnum which was very deceptive.

It turned out to be a slightly warped flange where the intake bolted to the block. ....You would think the gasket would compensate for the small amount of warpage I found, but resurfacing the manifold flange cured the problem.

I then checked the carb-to-manifold mountings, but they were OK.

(quoted from post at 19:34:45 05/29/15) Did you check the flywheel key?

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That was it! Had to sit and think about this. Once I pulled the flywheel bolt, I could tell and the key part was loose.

For reference, in the past I have always put a punch mark on the crank end to tell where center is so I can easily tell if it is sheared without pulling the flywheel.

This should get me all taken care of!

Thx!

On a Briggs 21hp twin I had something like this and it was the key. You find that the concave washer for the flywheels looses it's dish or bend a little and loosens. Fixed it with a big honkin lock washer! Bust FOUR keys in a row before I figgerd that one out!