I think this one was put to bed a long time ago, but I still hear it every once in a while. The notion that Honda (actually, Keihin) made the Keihin constant velocity carburetor tops and slides as a matching set. No, not so. Good thing, too.

First, the clearance between the top's brass bush and the slide's chrome plated shaft is not so meticulous that such pains as special fitting needed to be taken. We're talking five or more thousandths of an inch here, a specification that in the world of Japanese engines is quite large. Sloppy, even. Second, the slide's vacuum seal is itself very basic. This is not a high precision part. Labyrinth seals are fairly low grade seals, relying as they do on trapped air and not physical contact. Third, there has been over fifty years of folks mixing and matching, to coin a phrase, tops and slides with never an issue. Some have even used CB450 and GL1000 tops interchangeably, and these actually are slightly different designs, yet they still work well.