Chad - not all of the various B's have the same casting characteristics.
GUESSING: probably at some point in the life of the two with the non-functional pumps, they have been "rebuilt" by a commercial rebuilder. The commercial rebuilders "group" the parts together from many different carbs (whether it will work or not), and remove the tags so intelligent customers don't know what they are getting (or not getting).
This really underscores why I commented early in this thread that "marrying" parts from multiple carburetors generally results in disasterous results.
Some limit their interchanging only to those castings with EXACTLY the same casting number; but even this is questionable, as the casting number is the number for a "blank" casting. The blanks can then be machined in a number of different ways. The only really safe interchanging of castings is from two carbs with EXACTLY the same identification number AND engineering status code on the tag.
Just in the "for what its worth category", we have records of 137 DIFFERENT Rochester model B carburetors.
Jon.
