AHEM.... I'm still here!! ;-)
I upgraded to a 4-stroke Subaru motor and probably got in excess of 100 mpg, but not sure if I ever measured after a while.
Now I ride a Honda PCX150 scooter that's also supposed to get over 100 mpg, but I've tweaked it to go faster (around 75 mph), so I only get 70 to 75 mpg now.
When my boys are a few years older, I would've introduced them to a Golden Eagle Bike Engine (GEBE) kit.... but from what I understand, they're no longer in business. Is there any other belt-driven kits around??
TTFN... Ta ta for now!!