In 1974, the S2 was expanded to and replaced by a S3. In addition, each model year following was met with toned down performance in attempt to meet new emissions regulations. The H and S series ceased production after 1975, and the model line became the KH series in 1976, omitting the 750 from the lineup and leaving just the KH250, KH400 and KH500. The last year for US sales was 1977, with only the KH400 and the KH250 left in the lineup. Both models continued to be available in Europe and elsewhere until 1980. Stricter emissions regulation and advances in 4-stroke technology caused the demise of the Kawasaki triples in both cases.