Today I installed my spare Zenith on Henrietta ('29 special coupe) which I rebuilt using flow-tested jets I bought from Renner's Corner:
http://rennerscorner.com/carburetor.html
Once I got the float valve adjusted properly, she ran better than I've ever had her running! I'll probably buy another set for my other Zenith. The jets came with data indicating their actual flow rates (cc/min).
Incidentally, if you don't have Tom Endy's dissertation on rebuilding the Zenith carb, you can find it here:
http://modelabasics.com/Carb/ZenithC...l2011-2007.pdf
Dave Gerold also has a paper on performance-testing the Zenith carb:
http://www.durableperformance.net/PE...ODEL_A_Web.pdf
Mike