When exactly do the spark plugs fire in the 912ULS?

Bill Hertzel wrote:

Roger Lee wrote:

Simple answer. It fires every stroke. 

And it is way more common than you might imagine.
It happens in any engine that does Not have a distributor.
This would include most lawn mowers.
You can see the wasted spark happen in This Video.
Skip to 6:10 in the video if you have ADHD.

Also engines that aren't coil on plug.