There is a lot to reply to…
-No, they never came with fuel pumps or regulators. A properly functioning fuel tap will provide more fuel than the motor can consume.
-As mentioned, the vacuum port closest to the fuel petcock has to be used for the fuel petcock. The others have to be blocked off with the correct rubber caps. (Autozone vacuum caps will rot apart in weeks as they are not fuel resistant.)
-If you remove the “clean air system” on the valve covers, loop the two reed boxes together with a hose or buy a block off kit. Plug the giant hole left in the air box.
-Zephyr fuel tanks are notorious for rust. Like really really bad. So remove your petcock and make sure it isn’t full of rust particles. If it IS full of rust, then tear down the carbs all the way. (As in separate every carb body.) The fuel distribution pipes between carbs are where the ultra fine rust particles settle and then plug everything up.
-Thoroughly clean the carbs. (Jets, emulsion tubes, air jets, all of the many idle ports….all of it.) Check that the float heights are correct. The CVK32 carbs on the Zephyr use the exact same rubber o-rings and other parts as the Zx600a/b/c, Concourse touring bikes. So I found sites that sold complete Viton o-ring kits for cvk carbs that I couldn’t through Kawasaki.
-Verify that someone hasn’t put in a Sigma jet kit. The “cheap” jet kits require that you drill an extra large hole in the diaphragm slide. If done/drilled improperly, those carbs will never work properly ever again. (Pod air filters do not physically fit in the 750 Zephyr frame, so don’t try to go that route)
Factory Pro is the only jet kit for the 750 Zephyr that doesn’t require drilling.
-Zephyrs use a computer to control the ignition advance and not governor weights like the older 750’s. So just look to make sure the Ignition box looks stock and the wiring looks factory. If someone hacked another ignition box in, that would also cause high rpm issues.
My best guess is that you have rust plugging something up somewhere in the fuel system.
Let us know what you find.