I only saw this happen one time on a Kohler, but the flywheel was loose enough that it sheered the key and stopped when it hit something.

But it still had spark.

Have somebody else look for spark on a well-grounded plug when you crank from the driver's seat, as usual.

If you set the park brake, it should have spark regardless of seat presents. Unsnap the large white connector near the engine and recheck for spark. Or with the spark plug connected it will run a few seconds if there is fuel above the carb solenoid. If you have it then, something in the safety line or switch is likely. If no spark likely a coil. though it is worth pulling the shroud and disconnecting the kill wire from the coil to be sure.

Thanks baymee, But I know the flyee key isn't sheared, I have seen that on two push mowers before (not mine)

Thank you, tomplum, You are correct all the way thru. However, This morning, the engine started right up and I mowed with out incident for about 40 minutes, put it away and shut it down. So------? Did the fuel solonoid fail to open after being shut down hot? It started right up and mowed about 20 ft and stopped dead. However, that doesn't explain the no spark when I pulled the plug.
Or is it possable that the coil is somehow the villin?
About three months ago, I shut engine down to talk to the same neighbor, on the same lawn, for a longer time, The engine refused to start and there was no spark when I pulled the plug. About an hour later, it started and ran fine.
Any further thoughts will be appreciated. Thanks, coho

"About three months ago, I shut engine down to talk to the same neighbor" Maybe it's the NEIGHBOR! Seriously, if you confirm that there is no ground to the kill wire on the coil AND you have no spark, then yes it comes down to the coil. So you need to continue with the testing. If you are testing spark by removing the plug, then at least start with a new plug. Or have one with you, hook the plug up and be sure to ground the base well like baymee said. Coils definitively experience issues hot many times as they start to fail. For giggles, confirm also that the fuel cap vent is open.

Over the years I've seen coils fail when hot and then recover when cool. A real PITA to diagnose.

A bad connection from the seat switch to OPR #1 could cause a no spark condition.

IF the problem occurs again, try pulling OPR #1 and then check for spark. IF you have spark, that would indicate the coil isn't the problem.
Problem would then be in the circuitry between terminal A1 of the key switch, through the seat switch to OPR #1

Today I recreated the stop dead conditions. !. Mowed for an hour. 2.(Didn't talk to a neighbor) Walked away and left it alone for 15 minutes. 3. Tried to start it, dead. 4. Tried two plugs for spark, none 5. Unpluged engine kill wire.Still no spark on either plug. 6, Left for two hours.
Good spark on both plugs. Pluged engine kill wire back in and started engine. Thanks tomplumb. Will get a new coil here and change out prior to complete failure.
Guess I could measure the air gap, but ,tom would you know the factory gap and any cautions that might be pertinate?
Thanks again. coho

The gap is .010 for the coil, basically a regular business card is close enough. Plug gap .040". Once the shroud is off, take the time to blow through the shrouds around the head. The CV single is a nice engine, but they miss the boat on being easy to clean, so now is the time!

If you have ever tried to set the coil/magneto gap to flywheel, with a metal feeler guage---you'd know why we say to use a business card to set the gap! Well nigh impossible to use the guage.
A fellow stopped in one day and asked what type of feeler guage i used, as he was having trouble doing it with his metal guage.
I fished out my business card, handed it to him, and got back a fishey eyed stare, and an incredulous look.

or Rusty, you could use the right tool for the job, brass feeler gauges, and set the gap correctly.

The gap isn't really that particular. The card trick had been "taught" in service schools for decades really. Briggs and Kohler vary their specs by .004", Kawasaki by up to .008" that I know of. I think Tecumseh, you just whack it with a hammer until in runs right...
When the techs play with timing on the cart engines, they grind the holes in the laminations longer so they can pull the coil way out from the flywheel. Amazing they even run at all!

"The gap isn't really that particular"

Never once saw that in a tech manual, but I do see specifications for gaps.

If all one has in the toolbox is a pair of water pump pliers, a claw hammer, and a couple adjustable wrenches then a business card is the chosen tool.

When advising people who don't know any better I advocate the right way and then they can hack as much as they choose to. That practice cuts down a lot on posts asking... how do you remove a broken bolt?

Yah, but: Trying to get the gap correct between a round flywheel and rounded coil legs, is just about the worst thing i have ever tried to do. The business card conforms to the curve of the flywheel, and won't push the coil away from the flywheel, like the springy brass feeler guage does. But--you do it your way. I'm not a perfectionist at setting coil leg gaps, and after a bunch of tries to get it set correctly, i have gone to the business card trick!

Not bite'n lurker. You probably didn't know that Rusty's business cards are printed on BASCO .010" card stock, with a pic on the back of Rusty next to Fred G Stratton holding their shot guns w/Moe the water spaniel in the middle w/ a duck in it's mouth, now did you? Don't know what kind of duck, or what the particular spec was on that duck....

That duck tasted really good, in the pot next day! I got him about 20 years ago, and found the pic i took at the time, in an old album. figgered it'd look nice on my card! Rusty

Before credit cards used match book cover for such gaps like points ect...) (you know the freebies like Holiday INN and so on). I got old steel feeler gauge set with one brass or copper colored blade on it??? always wondered what the copper colored blade was for???