Then you can appreciate the pebbly bits!
I watched most of those videos. He made the 212cc engine go 50 MPH and 54 MPG, but not necessarily on the same run, and then swapped in a 420cc engine, but he wants to be able to go back and forth between the two.
I don't know if he modified the 212cc as much as possible, but he keeps modifying the 420cc.
The last video suggests he blew up the engine and ended the project, but then there seem to be more videos.
I wonder if I would understand anything he said if I were in full health.