Difficile de définir sur quelle base ce chopper a été construit. Ce qui est sûr c'est le pilote. Il s'agit de John Bonham, le batteur du groupe Led Zeppelin (décédé en 1980) The conical front brake is a BSA/Triumph item from 1971-73. I think the motor is also BSA/Triumph - a single cylinder - maybe a B50? Cool bike. Dual-square headlights were illegal in the USA back when this was filmed. I have found a better pic at www.led-zeppelin.org (not from the movie): It seems to be a single cylinder BSA with a one in two exhaust pipe.
A BSA expert tells me, "with angle of the carburettor, one would almost think BSA 250"