This wasn't Yamaha's first four-cylinder two-stroke though. In 1968 it had raced a 250cc vee-four which was an incredible piece of engineering, dishing out 73bhp at a shade over 14,000rpm, sported an 8-speed gearbox, twin ignition systems and an autolube system. A 500 was on the cards but at the end of the 1968 season the FIM played spoilsport and banned four-cylinder machines from the 250cc class in order to keep the costs of racing low. Yamaha pulled out of World Championship Grand Prix racing as a works team but crucially continued to supply bikes like the TD1s and TD2s plus their liquid-cooled successors the TZ250s to privateers. However the competition department had kept its hand in and thus was born the Yamaha 500cc challenger. In early tests, the reed valve inhibited maximum flow into the crankcases and for a while the reed valves were junked for tuned inlet tract length intakes. By designing the engine with the correct distance from the crankcase to the bell mouth of the carb, the shock wave that travels backwards and forwards along the tract could be employed as a valve that would ensure little gas could escape from the engine. However, the reed valved engine was used in the TZ500's first race and the men entrusted with the job of spearheading Yamaha's foray into the premier class were Finn Jarno Saarinen and Japanese rider Hideo Kanaya.