Harley Davidson is not famous for winning anything much in Aussie racing but they have a history in American flat track racing that will take some beating. From 1946 until 2016 the Milwaukee machines took home the bacon 54 times, with several multi year wins of nine consecutive years or more. The most famous model of that era is the XR750 known as being the most successful race bike of all time and also the one that Evel Knievel made his name on during his record breaking motorcycle jumping career. AMA rules set between the world wars allowed a maximum capacity of 750cc for side valve engines and 500cc for overhead valve ones, to even up the racing between the local product and British bikes. The 1946 crown went to Norton, HD took it home for the next four years and then Indian dominated until 1953 when it went bust. Harley then had a clear nine year winning streak with the side valve KR750 until Dick Mann on a BSA knocked them off the podium in 1963. Harley took the title for the next three years then it went to Triumph in 1967 and 1968 with Harley finally back on top in 1969. The XR750 had an actual capacity of 748cc and used two 36 milimeters Mikuni carburettors that took air in through pleated paper pod filters without any airbox. The iron motor had a bore and stroke of 76 milimeters x 81 milimeters while the later alloy one sported 79 milimeters x 76 milimeters dimensions, An output figure of 82 horsepower at 7700rpm is quoted. All the bang was fed though a triple row primary chain to a four speed gearbox with the wheels being 19 inchers front and back. All of that was housed in a steel, twin loop full cradle frame similar to the Sportster with the backbone tube reduced to one inch diameter for an all up weight of 134kg dry. Flat trackers don’t run front brakes and the rear was optional at the time, but why on earth would anyone say no to one, A major difference in the XR engine compared to other HDs was that it had four short camshafts inherited from the KR. These camshafts allowed better performance as well as a straighter run for the pushrods and greater adjustability of cam timing.
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