Seen some euro diesels VW19 TDI and XUD 19 citroen fours, Good engines but heavy.
The 3 cylinder PD 1422 TDI is a bit lighter its like a 19 four with a pot sawn off weight wise but its still heavy enough in a bike.
Enfield made a few diesels had a HATZ engine in them, was ok but possibly a bit underpowered for two up.
I very nearly got a diesel bike built in the mid 90s it was a 30s/40s girder forked rigid rear 125/150/ 200( Villiers type motors) exselsior frame wheelsc and tank with a farryman single cylinder diesel running through a pre unit bsa box , i acctualy had it built running in the frame had a seat rear brake and only needed exhaust some air filteration making and detail stuff which needed more time than i wanted to spend on it, i bunged it in an auction at a local fam i often regret not finishing it it rode quite well up the lane.

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