Les was riding a Jawa DT500 double overhead cam known as a double knocker, micheal Lee rode one when he won in 80, mauger and Olsen dabbled with them too, the introduction of the 34 mil carb literally killed off the DT500 overnight, it was a very thirsty engine that worked well 36 or 38 mm carbs,,ice racers used a 2 valve version, it was another couple of year before Jawa were back on the scene with the 897 single over head cam