A little while back we mentioned a Royal Enfield for sale that was set up to run on biodiesel. Here's a very well laid out website by Charles Altmann who shows you how to take a Royal Enfield Bullet, and after removing the gasoline engine, install a 406cc, single cylinder, direct injection Yanmar diesel or Yanmar clone in it's place. He has a lot of photos and even has diagrams available for the mount and adapter necessary to make it work. He even retains the kick start which he says works well once you get the hang of it.
You have to realize going into this project that once you're done you'll have a motorcycle that will compete with 50cc scooters on a performance level, ... that means slow, really slow, but on the other hand you can make your own biodiesel fuel and most likely operate this motorcycle at almost zero cost.
Charles Altmann has a little company over in Germany called Altmann Machines where he builds a lot of neat devices primarily focused on motorcycles and audio. This Royal Enfield conversion is just one of his motorcycle projects.
Since Royal Enfields and Yanmar diesel engines are readily available these days it looks like a neat project for someone looking for an environmentally friendly little scoot. Just remember to leave a lot of time between appointments.