Yes, you could think of the balance screw between the two sets of throttle bodies as the 'course' adjustment and the air bleed screws as the 'fine' adjustment as that is sort of how it works out. To be honest, I do not know why there is a balance screw, as you mention all four T.B.'s could be synch'd with the air bleed screws.
I can't tell from your posts but after each adjustment you should tap the throttle just a little bit to bring the engine RPM up and especially, reset all the throttle body throttle plates against their respective stops. Just adjusting the balance screw and watching for change will not work very well. But you also have to be careful not to 'zing' the throttle too hard as there will be a strong vacuum generated when you close the throttle and you do not want to pull fluid (especially mercury if you have mercury 'sticks' (manometers) ) into the throttle bodies from the top of the manometer tubes. So a gentle tap on the throttle followed by perhaps 5 or 10 seconds to let everything settle down and stabilize and you will notice a change after each turn of the balance screw.
You also have to tap the throttle slightly when turning the individual air bleed screws just to reset all the vacuum levels in all the throttle bodies. Also this adjustment is tricky because as you adjust any one screw, the other three T.B.'s will change and the changes may NOT be the SAME for all three. So you are trying to hit a moving target. The method is to make small moves and generally move toward an even vacuum reading.
Not sure what Kawasaki recommends but I think it is something like 5 cm of mercury difference between all four. With some tweaking you should be able to get all of them within 2 cm of mercury, and perhaps a tad batter but 1 cm is a lot to ask for in my opinion. Note that each reading is really only good for one throttle setting, temperature, etc. because when something like the idle speed changes, so will the relative T.B. vacuum balance.
As far as the actual value of each vacuum reading, you cannot control that- physics does. At a given RPM and a given set of conditions (temp., air / fuel ratio, humidity, and several others) there will be a specific pressure drop across the throttle bodies where the throttle plates are restricting flow (and causing the engine to idle). You can adjust the ratios but not the total amount; if you raise one value, the other three will make a corresponding drop and the sum will be the same within a reasonable idling range. The actual vacuum value is more indicative of engine efficiency (volumetric efficiency) and condition and even that is not a very good way to measure in my opinion. My advice is to ignore the actual value as long as it is not a long way from the factory spec. say, 10 cm of mercury or more. Just balance the individual cylinders relative to each other and call it great; trying to hit a particular value is not going to work and will drive you crazy trying.
Glad to hear you made out OK with the whole thing. Tasks like this are not nearly as scientific as, say, balancing a wheel and tend to be a 'hocus pocus' or best result kind of adjustment like steering a boat on the water rather than a precision setting.
Brian
I need someone with a good understanding on the TB Sync to chime in here.
After syncing both left and right (ie. 1/2 with 3/4) all 4 of my tb's were not in spec. They were all on the high side. The manual states to "balance 1 and 2" and then "3 and 4" with bleeder screws. Ok fine. Done. Still not in spec, all too high. Manual doesn't cover what to do next, so I assumed that adjusting each bleeder screw to bring down each tb into spec was the next step.
This got me thinking - why do we bother with the centre screw in the first place, if we could use the bleeder screws to put all tB in sync with each other and within spec? Am i making this too complicated? Is the center screw meant as a 'gross adjuster' and the bleeders 'fine tune'?
If one can adjust all bleeder screws so all TB are bang on 250mmhg is this not the point - what am I missing?