1978

In 1978, Kenny Roberts joined the Yamaha team, pairing up with Johnny Cecotto. In addition, Takazumi Katayama joined the Yamaha camp under contract with Yamaha's European group company, YMENV. The machine used this year was the YZR500 (OW35K), which was based on the OW35 with the YPVS exhaust device to boost performance.
Roberts, who participated originally in AMA dirt track racing, drew a lot of attention with his groove-less slick tires and "hang-on" riding style, in which he would hang his body over the side of the machine to the inside during cornering. This Roberts style would have a big influence on the future of riding styles in road racing. Roberts also competed in the 250cc class, merely to get acquainted with the GP tracks, and ended up astonishing many in the field by winning the opening round.

In the opening round of the GP500 series in Venezuela, he had to retire from the race in the early stages. After finishing 2nd in the following round in Spain, he found his form and won the following three races in Austria, France, and Italy. Roberts continued in good form, coming 2nd in the Netherlands and Belgium to gain a margin in the series ranking over his main rival, Barry Sheene (Suzuki). Towards the end of the season, Roberts took his fourth win in the British GP, which clinched the championship title for him in his debut year. Cecotto also performed well, with a win in the Netherlands and an eventual 3rd in the ranking. Takazumi Katayama ended his season ranked 5th. Yamaha and Suzuki were closely matched this year, with three riders each in the top six of the final ranking.

In the second season of the Formula 750, the series was reduced to 10 races. Yamaha competed with the YZR750, as in the previous year, and Cecotto took three wins to secure the title. Roberts won four races in the series, but ended up 2nd in the ranking. In addition, Yamaha machines swept the top 10 places in the ranking.