OK, I re-checked everything and found something really interesting. Thanks to Dan, I checked the stamps on the primary and secondary meter jets and, while they are correctly placed, they also say "Solex"! So my questions are: did Zenith ever use Solex parts, did someone probably make an incorrect parts swap (and does it mess anything up in doing so), or is the carb really a Solex and I've been trying to work a Zenith rebuild kit into it?! The caps on the secondary vacuum housings say Zenith, so that's what I've been going by, but I guess I really should check the numbers on the brass tab on the fron of the carb. Do either of you know where I may be able to reference these numbers to find out which carbs I have? Sherlock Holmes, eat your heart out...