A friend of me and i build 2 of these nice engines. They look 99% similar. We used castings from another friend who made them for us. The engine is no hit'n miss. We use 2 driven valves instead. We gave it an adjustable ignition which is not really necessary but looks cool. The ignition system is a homemade CDI and is hidden in the engine base. The engine almost starts on the first flip.
Video of the running engine: https://www.youtube.com/watch?v=5aNJIGtiRLY
Video of the running engine: https://www.youtube.com/watch?v=5aNJIGtiRLY
