Ok thanks, i also think that the engine is not original. I find on the internet: HONDA CB750K(RC01)
Framecode RC01 Year 79-82 Yearcode ZAB
Frame Numbers RC01-2000121-RC01-2300006
Horsepower 77 PS, 57 kw
My motornumber is between those numbers.
How can i find out that the bike was ever registred...