The Yamaha XS650 is a mid-size motorcycle made by Yamaha Motor Company. The standard model was introduced in October 1969,and produced through 1979. The "Special" cruiser model was introduced in 1978 and produced through 1985. The XS650 began with the 1955 Hosk SOHC 500 twin. After about 10 years of producing 500 twin, Hosk engineers designed a 650 cc twin. Later the Hosk company was acquired by Showa Corporation, and in 1960 Yamaha had bought Showa with Hosk's early design of 650 cc twin. When the Yamaha XS 650 was launched in October 1969 it had one of the most advanced engines in its class of large parallel twin motorcycles. The engine and gearbox are unit construction with the crankcase split horizontally for ease of assembly whereas almost all contemporaries in its class in 1969 are either unit construction with a vertically split crankcase or pre-unit construction with separate engine and gearbox. The XS650's engine was used in AMA Professional Dirt Track Racing by national champion Kenny Roberts. In 1969 only the Laverda 750S, and the Honda CB350, also launched that year, matched the XS 650's modernity of unit construction and SOHC valve operation. Model history The 1970 model was designated the XS-1. Subsequent Yamaha Xs650 models were XS-1B (1971), XS-2 (1972), then TX650/XS2B (1973), TX650-A (1974), XS650B (1975), XS650C (1976), XS-D (1977), XS-E (1978), XS-F (1979). 1979 was the last year of the so-called "Standards" (an unofficial term commonly used to differentiate it from the "Special," which has pullback bars, a teardrop tank, and other differences in appearance). The Es and Fs also came in Special form: XS-SE (S for Special) and XS-SF. From then on they were Specials only to XS-SG, XS-SH, XS-SJ, XS-SK. There was a Special II (Two) model designation in 1978 (unknown) in 1979 (XS-SF-II), 1980 (XS-G), 1981 (XS-H) which were models with fewer chrome parts decals instead of plated plastic on the side covers as well as drum rear brake and wire wheels versus disc rear brake or cast wheels. The Special II was offered until 1985, the last year for the XS 650. The first two model years (XS-1 and XS-1B) were kick start only, with an electric starter added from the 1972 model year on. This had a compression release added to the front left exhaust tappet cover resulting in a square versus triangular cover found on the other exhaust and intake