Two-wheeled Stanley Steamer.
Actually, steam is not as complicated or difficult to engineer as an internal-combustion engine, has excellent torque characteristics all the way through advancing throttle position, and because it is EXTERNAL combustion, virtually no NOx emissions and very little carbon monoxide in the flame exhaust. Extremely wasteful of water with no recirculation/reclamation system, however, with serious problems with water purity, as like an old teakettle, a serious buildup of lime begins to occur.
Abner Doble solved that problem back in the 1920’s, and the Doble steam-powered automobile was probably the most sophisticated design of its time. But Abner Doble was no businessman, and no two Doble vehicles were ever the same. He just had to keep tinkering and adjusting the kinds of innovations.
https://www.youtube.com/watch?v=rUg_ukBwsyo
With flash boilers and condensers steam is a very efficient mechanical power source.