直列4気筒
In 1968 the domination of the inline-twin engine for high-performance street bikes came to an end when Triumph Engineering developed an inline-triple engine for the BSA Rocket 3/Triumph Trident. The 1969 Kawasaki H1 Mach III with an inline-triple two-stroke, and the Honda CB750's Inline-four engine into the bargain, foreshadowed the ascendancy of multi-cylinder engines. The "W" series engines were oil-tight and reliable, but by comparison they had low levels of performance with high levels of vibration, and were ultimately unsuccessful on the sales floor. At the same time that production of the "W" series was ending in Japan, Kawasaki came up with a formula for successful four-stroke street bikes in its "Z" series.