Of course they can be had from eBay and other similar places, but my favorite service manuals in the world can also still be bought DIRECTLY from Kawasaki. Do yourself a favor and get the original before you look into other aftermarket manual vendors if you can…:

• The Kawasaki Service Manual for the ’74-’77 KZ400 (D & S), Part #99997-710-06, $36.96 (shipping included!)
  Click here to buy directly from Kawasaki
• The Kawasaki Service Manual for the ’76-’79 KZ750 (B1-B4), Part #99997-744-04, $36.96 (shipping included!)
  Click here to buy directly from Kawasaki

Manuals In Digital Formats

A note about these files: Some of these links for the manuals (especially for the larger files) are to an external storage repository (WordPress.com, actually) that behaves a bit strangely. It seems that the file download might take forever (like minutes or so) to start, but then starts downloading at a pretty good rate. I hope it works for you. I have tested it and it seems to work well for me….

• The complete “Kawasaki Service Manual” for the ’76-’79 KZ750 Twin (B1-B4), as ONE CONTIGUOUS scanned PDF file, thanks to EnHising of the THE KAWASAKI TWIN OWNERS FORUM: Link 1, Link 2, Link 3, Link 4. WARNING: This file is ~186MB, so don’t just click on it directly; make sure to right-click and choose “Save As…” or you will likely get an application error.
• The complete “Kawasaki Service Manual” for the ’76-’79 KZ750 Twin (B1-B4), split into INDIVIDUAL PAGES in PDF format, donated by Homer/Davie from KZRider.com: Link 1. NOTE: It was originally provided to me in DOC format, and it kinda’ got chewed up a bit in my conversion process to PDF (using OpenOffice)… after having been chewed up a bit from the OCR in MS Office in the first place… but I hope it helps anyway…
• The complete “Kawasaki Service Manual” for the ’79 KZ750 B4 Twin, **with supplements** for the ’80 G1 (a.k.a. LTD II) and the ’81 / ’82 M1 (a.k.a CSR), as ONE CONTIGUOUS scanned PDF file, thanks to George of the THE KAWASAKI TWIN OWNERS FORUM: Link 1, Link 2, Link 3, Link 4. WARNING: This file is ~195MB, so don’t just click on it directly; make sure to right-click and choose “Save As…” or you will likely get an application error.
• Here are pages 303-332 of the “Supplement 1983 KZ750-K1,S2,Y2″, split into INDIVIDUAL PAGES in JPG format, thanks to EnHising from the THE KAWASAKI TWIN OWNERS FORUM: Link 1.
• Here is the complete “Supplement 1983 KZ750-K1,S2,Y2″, as ONE CONTIGUOUS scanned PDF file, thanks to George of the THE KAWASAKI TWIN OWNERS FORUM: Link 1, Link 2, Link 3, Link 4. WARNING: This file is ~17MB.
• This one is not 750-related, but is for another rare twin; The complete “Kawasaki Service Manual” for the ’79 Z250, **with supplements** for: ’80 Z250 A2, ’80 Z250 B1, ’81 Z250 A3, ’81 Z250 B2, ’81 KZ305 A1, ’81 KZ305 C1, ’82 Z250 A4, ’82 Z250 B3, ’82 KZ305 A2, ’82 KZ305 B1, ’82 KZ305 D1.  It is ONE CONTIGUOUS scanned PDF file, thanks to Stealthwifi of the THE KAWASAKI TWIN OWNERS FORUM: Link 1, Link 2, Link 3, Link 4.  WARNING: This file is ~65MB, so don’t just click on it directly; make sure to right-click and choose “Save As…” or you will likely get an application error.