Z1OwnersClub GB

Hi there,
I recently bought a KZ900.1976 from America,the frame numbers fine,Z1F........but the engine number starts KZT00 instead of Z1E,is this normal?it has 903cc stamped on the barrels
If anybody can help that would be great

Could be a later z1000 bottom end....

https://www.z-power.co.uk/z1000a1a2b1b2-ltd

Z1000 cases with 900 top end.

Thanks for the input
Thought maybe the American kz900 had different numbers
Cheers