In 1974 Kawasaki launched the new "S3" 400. This replaced the S2 350 in their two stroke triple line-up.
In 1974 Yamaha had the RD350, Honda the CB350 and Suzuki the GT380, The S3 was introduced to one up them.
Unlike the poor gas mileage of the S2, H1 and H2, the S3 made excellent gas mileage. In comparison to the 1973 S2, it averaged well over a 10mpg improvement.

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1974 S3 400 Mach II
Frame Number Range: S3F-00001
Engine Number Range: S3E 00001
Colors: Candy Red / Candy Sky Blue
Side covers Have Mach II under the 400 badge

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1975 S3A
Frame Number started at S3F-14300
Engine Number Range: S3E 14300
Colors: Candy Green / Candy Super Red
Side covers no longer have Mach II under the 400 badge
6 bearing crank

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1976 KH400-A3 
Frame Number Range: S3F-26200
Engine Number Range: S3E 26200
Colors: Candy Red, Dark Green, Orange, Brown
​Frame Was strengthened at the steering head and near shock mounts
CDI ignition
Designed to run on low octane unleaded gas
9" front brake disc

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1977 KH400-A4 
Frame Number Range: S3F-33601
Engine Number Range: S3E 33601
Colors: Candy Emerald Green / Candy Purple

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1978 KH400-A5
Frame Number Range: S3F-42801
Engine Number Range: S3E 42801
Colors: Candy Persimmon Red / Candy Lime Green
Not sold in USA

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1979 KH400-A6
Frame Number Range: S3F-45901
Engine Number Range: S3E 45901
Not sold in USA

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1980 KH400-A7
Frame Number Range: S3F-46601
Engine Number Range: S3E 46601
​Not sold in USA

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