Kohler 13hp in a Cub Cadet 2135 Yard Tractor. New: carb, oil(and filter), spark plug. Cleaned and lubed. Ran great the first mowing after maintenance, about halfway through the second mowing, started chugging and vibrating oddly(an odd sound, almost like a loose hood or side cover, but not exactly), PTO off, calmed down, leveled mower, PTO back on, same thing. Tried letting cool for about 15 minutes, started fine, PTO on, same thing. Let sit for 30 minutes, now won't start at all, not even an attempt to fire. Has spark(though it seems to be a constant white spark), checked compression(is good), and looked at valves(moving fine). Thinking ignition module, any other ideas?

Hi,
Sounds like a failed spindle on the deck. Say that because it acts up then. Try checking the blades(and spindles for easy rotation) with the engine off. If it has an electric PTO clutch, there will be some resistance, but it should be uniform. If it feels rough and different at any point then it is time to get the belt off the clutch to verify which has failed. Usually available as a unit, but only from a Cub Dealer. May be aftermarket options.
Peace,
Clarke

Thanks for the reply crigby.

I had originally thought there might be an issue there as well, but when it refused to start at all after giving it cool down time the second time, I figure that's not it. I found some notes about testing the ignition module, and will pull it and try it and see what I get.

Hi,
Might try simply a new plug. That engine is also famous for sheared flywheel keys if they are shut off at full speed. Will still have fire, just at the wrong time.
Peace,
Clarke

Hi,
Might try simply a new plug. That engine is also famous for sheared flywheel keys if they are shut off at full speed. Will still have fire, just at the wrong time.
Peace,
Clarke

You know, it's a new plug so I hadn't thought of trying another just to make sure it was good. Will do, thanks for the suggestion.