I poked around a bit more on that site, and was fascinated by the torque output curve on a single-cylinder engine. I knew it wasn't particularly smooth, but that curve was worse than I thought.

There was also some information about belt-drive systems, with a brief reference to one on a Harley. I was interested to see the picture of the toothed belt, broken, with the cause of failure diagnosed as running the belt with inadequate preload (fancy words for too loose).