I have a couple of 18HP Kohler Commands in my 1862 and 1864 Cadet mowers with 46" decks along with (4) 17 HP Kohlers in older Cadets. All of them seem to run "rich" at an idle. You could have several problems.

If you noticed debris in the carb and changed the fuel filter, some residue is likely in the fuel line between the fuel filter and carb and you may be recontaminating it. Getting junk in the carb affects performance and can keep the needle valve and float mechanism open a tiny portion causing some flooding. I'd suggest cleaning it again and flushing the line between the filter and carb. I would also suggest replacing the needle valve and seat since they are not that expensive. It is a common engine so these parts should be easy to get.

Another component is the air filter, if it is clogged sufficient air can't mix with the fuel.

My dealer told me that the Kohler engine has fixed porting so you can't change the fuel mix at operating speed but can play with the idle adjustment.

If you turn this model off quickly after doing some work without a 1 to 2 minute idle cool down, it generally will backfire and diesel.

If I remember correctly, there is a screw for idle adjustment that controls the idle RPM. There is also a governor adjustment which is a spring attached to a lever. There are several spring attachment points. I wouldn't mess with that unless you think someone has been messing with it earlier. If while idling, the governor is substantially reacting to keep it running, it is out of adjustment.

If you have a carb that has an orifice adjustment, you can turn it in until it begins to run rough, then open it counting the screw rev's until it runs rough again. Then turn it back into the middle position or half the screw rev's.

If it is running too rich, tighten the screw until is runs rough and then back up the screw position 1/4 to 1/2 rev.

Those are the two steps my dad taught me. If that don't work, step three is take it to a good lawnmower shop. There is nothing wrong with the Kohler that can't be easily repaired. My commands have about 500 hours on them and my old 17 HP's have up to 1700 hrs.

P.S. Many engines run differently in winter months running especially "rich". One of my 17 HP's exhibited a carb freeze-up situation until the air intake got a flexible hose attached to it warming it up from a bracket on the exhaust manifold to preheat the intake. You could actually see the frost build-up on the outside of the carb, the float would stick open and just dump gas. It would go through a tank of gas in less than an hour and wash down the cylinder walls and collect in the pan. The pan would fill up until the engine wouldn't run anymore.

Hope this helps!

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