that blast would be great if you were the size of a horse jockey. Very cool idea and would be cool to have in the garage. 100 mpg! I wish I had the know how to do stuff like that. I have 37 years to learn I guess, because I have 37 years until I can retire.
You wouldn't need more than 12 hp even with your 240lb ass on it for town work, cos it's got enormous gobs of torque for it's size & a CVT, so there's no shifting lag just continuous acceleration. Not sure I'd want to run the dragon on it though. Those little Yanmars are a good lump, a friend had one in a 11 ton sailboat & it was as good as the old 1.5l 4 pot BMC engine that came out. They're used a lot here in plant machinery, mini-backhoes & such.
I tried for 2+ years to get my Swedish partner at Highland, AB to start a project developing lightweight 1 & 2 cyl. high performance diesels for the power sports market. To no avail.