Michael Waller of Britannia Motorcycles videos' a whole series of a C15 Trials build. BM250 he calls it. Frame construction through test ride.
sorry if its a repeat...but very interesting! he's running the knock-off, of the knock off, of the PWK carb! (that part is 14min. into video #17)

https://www.youtube.com/watch?v=aekA028QVLg&list=PL-f-b3vlEx-xuG5ZGyDvs3Tt7aUYl9gOf

enjoy! sorry if this is a repeat post in any way....