TOPIC:

Since I've been dragging my feet on this bike, I can't remember things I've done.  Now, I had these carbs rebuilt for one of the parts bikes I have. When I bought the running bike, I wanted to rebuild the carbs on it.  Putting it back together, I find I don't have this part.  It's not on either of the rebuilt carbs.

It's a 79 Shaft model.  I think it would be odd that Kawasaki wouldn't at least put a cover on it.

 

That float bowl is cast for two diaphragms: one is a pump diaphragm, which is lower down on the bowl, and that second chamber, which is for...I'm not sure what.  It somehow interacts with the vacuum in the system.  The second chamber is only used on a few carb models, and frankly, from what everybody says, it doesn't work for crap and causes nothing but problems.  
Bottom line: be happy that your bowl isn't drilled for that feature.  It's not a benefit.  

That is the unmachined sensor diaphragm casting on a set of Mikuni VM28's.
No cap needed or was ever fitted to those carbs so nothing is missing..

K&L sells an accelerator pump kit that includes the vacuum diaphragm which it isn't needed on your carburetors.  If you look at the kit, the vacuum diaphragm has a long shaft or pin. That pin is supposed to slide into a hole in the middle of the triangular flange, but as already mentioned, yours isn't machined.  Most if not all 79-on models don't use the vacuum diaphragm. My 81 KZ650-CSR doesn't. not sure about earlier models.

www.z1enterprises.com/accelerator-pump-kit.html

Thanks, guys.  That's exactly what I wanted to hear.  Yes, the K&L kit came with both diaphragms.  Now I can reinstall them without the worry that I'd have to hunt something down and try to put it on when the carbs are installed.