br The 1975 AMA 500cc National Championship Series will go down in the history of motocross as one of the most exciting in the sport’s history. With only five races in the series that year, there was little room for error. It would all come down to the last race in New Orleans on a hot humid day in September, 1975. Jimmy Weinert, Bill Buchka, Brad Lackey, Forti and Bob Hannah.