Well - I can sure as **** see the attraction! Lower RPM, gobs of torque, and far better fuel efficiency... Seems as if a diesel would be far better suited for this application than the average 2 stroke.
This was a common theme with ultralight aviation too, a diesel is far better for spinnin' a prop than the almost mandatory two stroke for all the above reasons. There were some noises about power/weight ratio but mostly the problem was the same as with our bikes...
They're simply not readily available in this country
While pretty common in Europe (particularly England) we never found a company there that would ship one to us. I haven't looked specifically for a diesel appropriate for our bike's needs - I'm sure they exist somewhere, in the correct size/HP anyway but prolly not set up to bolt in the frame lol
If anyone hears of something that might work - defo gimmie a shout