what 28mm carbs will fit my 650?

building up the z650 motor with some high lift cams , ported head and a small bump in c/r. has kerker pipe
by my calculations i need some 28mm carbs for max power from the combo i'm running.
what do i need and from what bike am i going to find them on?

Mikuni vm28 carbs would be the way I'd go. They came stock on the early z1 (some of these parts are hard to come by though so I'd look for a later set), also on some of the kz900/1000 bikes (sorry, don't know for sure what years/models came with the 28s and what came with 26s) Your carb body spacing will be the same on any of these and will match the intake spacing on the 650's head. You will need to get bigger carb holders. Get them for a late kz900 (IIRC I bought them for a 77 kz900 when I put my 26s on my 650). You'll also have to slot the mounting holes on the carb holders so they'll bolt up to the 650's head, and sand off the "lip" on the back side of the carb holder that rests inside the 900/1000 head. Use a light layer of black silicone between the surfaces to ensure a good mating.

The 78 Z1R also came with 28s and so did some of the later bikes before they went to CVs

550, 650, 750, 900 and 1000 have the same spacing

Not the 550. those are quite a bit closer together. The 550 however has the same spacing as the 750 zephyr. What is nice is to get a set of 750 Zephyr Manifolds and mount a set of CVK 32mm Keihin's on the bike. The manifolds will bring the spacing down to the 550 spacing. There is where you get the real nice performance. That is a nice mod for any 650-900 engine. Maybe even larger.