Running rich when NOT under load

Pull the engine cover and the flywheel nut and do a quick check of the key.
The 2 halves of the hole should form a perfect square if not pull the flywheel.
As we have stated many times we only have what you tell us & show us to go on.
Usually a partially sheared key will advance the engine which exhibits different symptoms to being rich.
However a retarded ignition will cause some black smoke as the fuel will not have time to burn fully.

At this point in time looks like we will have to start looking at outside possibilities.

I pulled the flywheel Friday and checked the key and it was fine. I'll take the nut and washer back off and snap a picture. I've got the inline ignition tester and I'm going to try to check it as well.

Well, I hate the taste of crow but I'm glad I followed your advice to recheck the key. I don't think this was the initial problem because it won't start at all now and I don't think it would have been running at all before. I think the key got like this when it started backfiring. Perhaps the loose valve lash had something to do with the initial problem. Still not sure how the valve lash got so far out of what, particularly since the nuts were still very tight. I don't have any extra keys so I'll pick up a few on Tuesday and hopefully between that and the loose valves that I corrected I will see some improvement. I'll keep you posted and thanks again for the advice.

On a positive note, at least I have one heckuva clean carb now!

I won't to confess how many times I have failed to tighten the flywheel quite enough, had a backfire sufficient to break the key then spent many hours trying to find the "other" problem.

I was able to pick up a key today. I went ahead and pulled the head and checked for sticking valves. The valves looked great, closed tightly, would not let any fluid pass when seated. I rechecked the valve lash and it was good. I replaced the spark plug again with another new one just in case I had a bad plug. Buttoned it all up and it started right away and ran smooth as silk for about a minute. As soon as it warmed up it started the same thing as before, sputtering at high idle with no load. Every few seconds it would sputter and spit out some black smoke. When the PTO was engaged it smoothed out. The sputter was still there but barely noticeable. I checked the spark with the inline tester. The spark was intermittent when it would sputter. Barely noticeable but not a smooth consistent spark. So...was the spark intermittent because of the sputter or did the intermittent spark cause the sputter? I made a short video where you can hear the engine surge/sputter and see the inline tester. I don't know of any way to upload a video though.

I've about ruled out the float, if it were the float it seems like the problem would have been consistent from the initial start, not a minute later after the engine is warm.

I'm really leaning toward the ignition coil at this point. Am I on the right track? Anything else I should check before I mortgage my house for a new coil?

Part number if you need it 21121-2069 $45 to $62.

That was going to be my next question. When I look it up I see two different coils, both claiming to fit that engine. The one you listed (21121-2069) and 21121-2086.

My engine code is FC540V-DS15. The 13 digit code on my mower is M0G235A070034. It's a single cylinder 17hp Kawasaki.

Based on what I saw I was thinking I needed the 21121-2086, which of course costs twice as much. For some reason the DS15 model is difficult to find parts for. That's what led to my initial problem of finding the right main jet for that carb.

Can anyone confirm?

Stens , Rotary & Prime Line all do aftermarket coils for your engine.

I have used all of them at different times and never had a problem.
Prime Line tend to be the cheapest and their gear has never let me down to date.

Bert, are you leaning toward the coil being the culprit?

Which coil (part #) for that engine?

Yes, that is what the spark test is for.
AT full speed the neon tube testers glow full red.
A misfire or two should not slow down the engine enough to cause the steady red light to flash.
So if you are getting flashing light co-inciding with the misfire the coil is breaking down.
However before you trash the coil you do the same test with the cut off wire disconnected in order to exclude troubles with the mowers wiring.
There are a lot of places to get a random ground short from.