Hey Joe and Bambi,
I believe that the answer is kinda like you are saying Bambi.
But in order to get a clearer picture, we all should just step back in time several years for the answer
......Back in the old days
before fuel injection was used everywhere, I am picturing a 4 cylinder Japanese bike that had 4 separate carbs.
From the throttle came 2 cables....1 pull on, and 1 to pull off. No springs here at all.
These cables went down into the inards in-between the line of 4 carbs and mounted up to 1 linkage.
Then this 1 linkage bar attached to each carb by way of an individual rod complete with adjusters on both ends
so you could at least get all carbs adjusted separately for idle speed and to make sure the slide opened fully.
There were adjusted on each end of this rod to allow those 2 actions to happen. And the return springs existed on each rod.
(the pic that kellymac posted displays this rod/adjuster concept)
HOW IT WORKS:
You simply set the slack for the cables first.
The main rod that goes crossways moved all of the individual rods the same distance. Any adjustment for individual carbs was accomplished separately. The bikes tuner simply just went down the line adjusting the rod/adjusters for each carb separately.
And you could set the spring resistance individually too.
And the pros would then put a tach meter on each sparkplug line and then fine-tune set the idle for each cylinder.
I don't have any 4 cylinder carbed bikes to show you, and my 86 guzzi Le Mans is all wrapped, packed, and covered
for the winter, so I cannot help with pics at all.
I am sure something like this could be built & tie the 2 carbs together and get what you are after.
Hope this helps