Engine Kohler Courage cranks hard, won't start, backfires through carb

Hello All

I have a Husqvarna riding mower with a Kohler Courage 21 (single cylinder). Unit is about 5 years old. Engine died during mowing session, would not restart then, or since. It cranks very hard, the flywheel just moves a couple of teeth, have to key the ignition several times to get it to make one complete revolution. Am powering from car so it's not a battery issue. It pops and/or backfires through the carb but nothing else. I have the air cleaner off and it's definitely coming through the carb.

Fuel and spark are good. I have removed the plastic fan cover to inspect the flywheel, the woodruf key appears to be intact. Any thoughts? I am guessing this is a valve issue but not an adjustment problem, sure, the valves are probably out of adjustment after five years but it was running fine prior to this, then it just stopped dead and now won't even crank. I don't think improper valve clearance will go from running fine to completely dead in one shot.

Any thoughts/suggestions would be appreciated. Right now I am just trying to diagnose how bad the problem is.

Thanks,
John

Have you tried taking the plugs out and spinning it over by hand to see if anything is binding?
Go ahead and pull the valve cover and see whats going on when you try to turn it by hand.

:welcome:
When was the last time the valve lash was checked / adjusted ?
What does the oil look like ?

If it spims freely without the spark plug then either the valve lash is way too big or the decompressor on the inlet cam is deceased.