According to the "Honda Motorcycle Identification Guide" Published by American Honda motor company:
* Cataloging purposes - Example: CB750/CB750K0
"K0" to indicate the first model in a series. If updated versions were introduced K1, K2, K3, etc... were used to indicate new models.
Beginning in 1968 with the CB450K1, and extending through the 1975 model year, "K" numbers often but not always, changed on an anual basis. In later years, various model designations were used to indicate model changes. Examples include CB350F1, CR250M1, CB125S2, Etc... The "K" number designation continued to be used outside the USA through 1978.
In 1974, Honda officially adopted a "Year Model" policy.
End reprint typing.
The F and K reference is definately a model difference. The CB550s had K0-K3s as well as F0-F2 (for the Super Sports), for example.
It is coincidence that the K designation for the CB750 happened to follow the model year of manufacture, I.E. a K2 was a 1972 model, K5 was a 1975 model. Other bikes don't follow this coincidence. A 1974 CB550 is a K0, 1975 CB550K is a K1, 1976 Cb550K is a K2. In 1975 the F models were introduced as F0, F1 and F2 for consecutive years of manufacture through 77.
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