My Kohler cv16 was running great for many years when out of the blue it backfired and never started again. It has great compression numbers and has relatively low hours. When it tries to start it shoots fireballs out the carb. I have replaced the woodruff key more than 5 times and it just keeps shearing as soon as it fires once (if it does). I've replaced the carb. I'm thinking it might be the "SAM" box, and that it no longer is working as its supposed too. I'm pretty sure its something related to the ignition system. The motor has been apart many times and many parts have been replaced. The cam shaft timing is still in sync. If anyone might know what's going on I'm open for suggestions. I'll be scraping it otherwise.
Start by cleaning up the flywheel & engine key slot they will probably have burrs on them.
Once the burrs are gone using some fine valve lapping paste lap the flywheel to the crankshaft
I usually go with fine paste then brasso ,
Reassemble and rotate the engine by hand
put an index mark on the engine & flywheel at top dead center
Now rotate the engine while watching the valve movement to confirm they are opening & closing at the correct time
