I worked on a friend's Kohler engine for their ZT mower that acted like this about 15 years ago.
It ran rough and was down on power.
Going from memory.
Yes, both cylinders were firing, but ONE of them was firing at the wrong time.
I found this out when I tested each cylinder with a timing light.
Though there were two magnetic pickups (one to fire each cylinder at the correct time), I found that both plugs were firing at the same time.
i.e. one was firing at the wrong time.
When I checked the wiring of the magnetic pickups, I found that on one of them, the connections looked OK but were flaky.
I cleaned up the connections, and reconnected them.
AFTER that the engine ran smooth, and when I connected the timing light to each cylinder, they were now firing at different times.
For some reason, with one of the magnetic pickups having flaky connections, the ignition system was using the one pickup with a good connection and firing both cylinders off of it, with one cylinder firing at the wrong time.
The engine has run fine ever since.
WHAT CAUSED me to look at the ignition connections was, the Kohler engine service manual said
"Reported ignition problems are most often due to poor
connections.".
And on THIS engine that was the problem.
YMMV
It ran rough and was down on power.
Going from memory.
Yes, both cylinders were firing, but ONE of them was firing at the wrong time.
I found this out when I tested each cylinder with a timing light.
Though there were two magnetic pickups (one to fire each cylinder at the correct time), I found that both plugs were firing at the same time.
i.e. one was firing at the wrong time.
When I checked the wiring of the magnetic pickups, I found that on one of them, the connections looked OK but were flaky.
I cleaned up the connections, and reconnected them.
AFTER that the engine ran smooth, and when I connected the timing light to each cylinder, they were now firing at different times.
For some reason, with one of the magnetic pickups having flaky connections, the ignition system was using the one pickup with a good connection and firing both cylinders off of it, with one cylinder firing at the wrong time.
The engine has run fine ever since.
WHAT CAUSED me to look at the ignition connections was, the Kohler engine service manual said
"Reported ignition problems are most often due to poor
connections.".
And on THIS engine that was the problem.
YMMV