So, I know where this air hose goes..  It comes from the air box, and then connects the all of the 4 TBs together.  What purpose does this really serve?  Would it be so bad to just plug those up?  It seems redundant as the four big tubes on top of the TBs also come from the air box, and is really just another possibility for an air leak.  I know there is an oil separator in the air box, but the hose that goes to the back of the 4 TBs doesn't come from the oil separator (as it shouldn't).

air / vacuume balance tubes perhaps
as each cylinder sucks there is a big vaccume difference between ...does this help equalize at certain rev ranges and add torque

there are similar things on many exhaust systems

The hose that is connected at the rear on all four TB's, is the gas/air return from
the cyclonic oil separator.

Riiiiiiggghhhhttt I remember now.  So, (basically), the way the oil separator works is that it collects oil / oil vapor from the crank case vent hose, which drops to the bottom of the separator and then goes back in to the engine, while the air / gas vapor goes to the top and then to the TBs.  So that is actually hooked in to the oil separator.   Thanks, Inge!

When I bolted up the 35mm throttle bodies from a K1100 to my 8V K100 I plugged all of those potential vacuum leaks with large rubber caps.