I have no known history of this bike.
Reg Lockhurst was a well known rider and he (or Weslake?) constructed a fourvalve conversion kit that put some more speed into the Jawa 890 twovalve engine.
Weslake made those heads for Lockhurst.
See pictures
I will go to Veterama in October and can deliver the bike there or elsewhere depending of where elsewhere is.
Price 2400 euro.
