If you want to know more about Harley's, this is a good video.

https://www.youtube.com/watch?v=XeuXShFIgyc&t=118s

In Harley's case, 2 pistons are mounted at the same point on the crank shaft, so the firing has to be 45 degrees offset, since the cylinders are 45 degrees offset.

Harley also fires both spark plugs at the same time. These two factors lead to a different sound when comparing it to other bikes.