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Ok, here's some REAL noob questions.

What carbs do I have on my stock '78 KZ650-B? How can I tell?

I see a rebuild kit I can get with 90, 97.5, 102.5 & 105 MAIN JETS, how do I know which ones to use?

I don't think they have been tampered with before. I've owned the bike since the early '80's and I haven't changed jets or needles. I've had them torn down for cleaning twice and didn't touch main or pilot jets.

I'm pretty ignorant about jet sizes and other issues. I just put them back the way I found them.

I think that all the 650s came with Mikuni VM24 carbs. Some 650 riders will jump in on this an correct me if I'm wrong. Don't know about jet sizes for those carbs.

if they have the horizontal (left-right ?)ribs id say 24s also.

I'm not too sure what we mean by "ribs." I think I recall vertical fillets on the outside to strengthen the slide cylinder. These are sort of triangular, but they are taller than they are wide.

Ribs are horizontal bands cast into the carb bodies. I suspect they may be for strengthening.

By George, I never noticed that before. Mine have the 3 ribs ringing the slide cylinder just like the ones in the wiredgeorge photo. In fact, the assembly in that photo could have come right off my bike.

My manual says that stock jets on the VM24's are 102.5's

Be careful with giving main jet sizes for VM24s... some had #90.5 mains and the largest was #102.5... this was for the 77 variation as I recall and later (79/80) had smaller main jets. It doesn't do much harm to use #102.5 as a baseline for jetting those carbs as the smallest sized main jets #90.5 are just too darn small for even the stock airbox in my opinion. The #105s in this kit were never used on any stock VM24 application.