I currently have a 74 honda CL200 that I don't have time to ride much anymore, it will probably be for sale in the spring. I've always had old Hondas. Formerly - 77 cb550, 72 cb350, 71 cl350, and a cafe 76 cj360. I also have 2 yamaha LB80 chappy's, and for a couple of summers I had a Suzuki drz400s with a couple of huge pelican boxes mounted on a custom built rack. That was before child, when I had dreams of doing some adventure riding. Most of the time my adventures were just to work and back. For me, It's getting harder to justify owning a bike- there's no room for a car seat!
As far as diesel bikes go, I have seen a couple of hacked together rat bikes at local shows, using an old military generator motor and a hatz pull start. Never seen anything I'd ride faster than my chappy!