Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/1224843
R I D E R E V I E W P68 ROBERT S FAMILY WORLD CHAMPIONSHIP BIKES day. And that narrow power band would have meant the OW48R's extractable gearbox was a key element in its championship success, with the art of setting it up just right in terms of the right choice of ratios for every circuit (Kenny had a choice of four possible ratios for first and second gears, and three each for third and fourth) really critical, with zero over-rev on an engine that's all done at just over 12,000 rpm. Kenny Roberts really had to work hard to earn the third of his world titles, and the key element in allowing him to do so was the OW48R Yamaha's more assured handling package—but 40 years on, nothing has changed. During the MotoGP era, Valentino Rossi and the now-retired Jorge Lorenzo won a succession of MotoGP world titles for Yamaha on a well-rounded YZR-M1 that, whether in 990cc or 800cc guise, always han- dled better than its Honda and Ducati rivals, while only rarely being as fast. So, just like nowadays, the key element in making the last of the piston- port YZR500 Yamahas into a world champion was the man who rode it. King Kenny, we salute you. systems, where you can't feel what the front tire is do- ing because the hydraulics dial out front-end suspension response when trail-braking into a turn. Here, you can. On The Pipe There's no denying that the OW48R's piston-port engine simply doesn't feel as power- ful as the more explosive disc-valves motors of the Kawasaki and Suzuki, even if the YPVS power-valve sys- tem does help max out top- end power, without doing so at the expense of ride-ability. Just as KR was later to tell me himself, I found you can't crack the throttle wide open at low rpm exiting a slow turn like the Assen Nationale Kurve, or else the engine will bog down and struggle to get back on the pipe. It'll pull okay on part throttle from as low as 6500 revs—but get it revving above 8000 rpm, keep up the turn speed, and you'll be rewarded with good drive by the standards of the day, as well as a smooth transition into where you really want to be, in the strong power band above 10 grand. From there to the engine's peak at 12,000 rpm the power builds pretty strongly, though not in the same eager way as the rotary-valve bikes—engine acceleration is more progressive and user-friendly, but also not as fast. In fact, Everett had fitted a set of later 38mm TZ500J Powerjet carbs to the Roberts bike, because they make more power on back-to-back dyno tests than the factory magnesium flat-slide carbs which came with the bike, which are also much harder to set upright, as well as to jet prop- erly on the day. But even with these, the Yamaha definitely wasn't as fast as Chris Wilson's ex-Kork Ballington KR500 Kawasaki I happened to be riding later the same Kenny chills with Aussie Kel Carruthers, the man he credits with helping him to his three world titles.