Bing 64 vent nipple position

More than acceptable!

The photo is right out of a factory assembly manual.

It would be preferred if each vent were to attach only to its associated carburetor.

As the Filters become restricted (Dirty) you would not want the imbalanced pressure on one side to vary the mixture the other.

OK, "acceptable", but does "more than acceptable" mean preferable?  If so, why?

The purpose of the Vent tube is to equalize/match the pressure within the float bowl with the pressure in the throat of the Carburettor.

The presence of an air filter produces a small and almost negligible drop in pressure when the filter is New and Clean.

As the filter does its job of collecting atmospheric dirt/dust/debris, it becomes more restrictive causing larger pressure drop through the filter.

This lowers the pressure in the throat of the carburetor causing more fuel to be pulled through the metering jets producing a richer mixture.

A restricted filter passes Less Air and draws more fuel.  The filter restriction acts as a virtual Choke.

If the Vent tube is attached such that it can communicate with the pressure WITHIN the air filter,  as the filter slowly becomes restricted,  the pressure in the carb throat and the pressure in the float bowl both reduce equally.

This makes less Air available to the engine but also proportionally less fuel to match.  The mixture remains constant. The restricted filter acts as a virtual Throttle Valve.

While a restricted filter is not a good thing as it reduces the power created by the engine, the choice of a virtual throttle reduction is much preferred to having a virtual choke applied.

It is not just Preferred and Acceptable,  it is Highly Preferred and More Than Acceptable! 

Bill I hope you n Roger are making some do-ray-me for all the good advice you share w/ all of us.

b- well  /  jg