Real head scratcher.

[PTmowerMech]

Kohler SV720S Twin Courage 23hp.

Both modules are firing. Unplug #2 plug (drivers side) and it fires up and runs on the #1 actually pretty smooth.
Plug in #2 and unplug #1 and engine just turns over, but no crank.
#2 plug is dry.

But the carb is a single barrel carb. Just inside the intake, it's wet on both sides.

Both plugs are good. (Not new)
I've adjusted the valves earlier and replaced fuel filter.

Compression test on #2 cylinder was over 200lbs. While #1 was about 150.
Thermal temp test was 350 plus on #1. About 150 on #2.

How is this even possible that if both mudules are firing, and it's a single barrel carb, could the #2 cylinder not be getting air and fuel?

 

[ILENGINE]

I would remove the plugs and and valve cover and turn the engine over by hand and make sure both valves on the cylinder that is not running properly is opening both valves the same distance.

 

[PTmowerMech]

Roger that, ghost rider. Both were the same.

Not sure what fixed it. But it's fixed.
I removed the carb and intake. Cleaned the surfaces. And revealed both ends of the intake (and carb).
Put everything back together. Fired it up for a minute or two. Killed it, removed #1 plug wire, and tried it again.
After a few seconds, #2 fired off and ran.
Plugged in #1 wired. Fired it back up and it runs better.

 

[tom3]

Did you ever swap the plugs side to side? Have had almost new plugs go bad like this, strange as it sounds.

 

[PTmowerMech]

Did you ever swap the plugs side to side? Have had almost new plugs go bad like this, strange as it sounds.

That may be what happened. I didn't label the plugs. Just put them aside til I needed them again.