Carbs used on Model Js
Just a clarification on the carburetors employed on the Model H and J Whizzers. The Model H made exclusive use of the Tillotson ML5B - no exceptions. However, the Model J employed both the ML5B and several different model Carter carbs. The Model J started out using the Carter N665S & N666S (fixed main jet carbs) for ~ 30,000 units, then used about 6,000 Tillotson ML5B. The ML5B used on the Model J differed from the one used on the Model H in that the carb flange mounting holes were elongated to allow fitment to both the Model H (1-5/8" spacing) and the Model J (1-13/16" spacing). Thus the ML5B provided carbs for Whizzer to mfg while Carter altered their design from a fixed main jet to an adjustable main jet model - N703S & N704S. Even after the introduction of the Carter adjustable main jet models, ML5Bs were still used on a limited range of Model J serial numbers (likely to consume the inventory of ML5B).
So if you have a model J with an ML5B on it, it is very possibly the correct carb. See info below for correct Model J carb by engine serial number. I own 2 such Model Js fit with ML5Bs.
Model J - SN 200,000 - 230,200, used Carter N665S & N666S
Model J - SN 230,201 - 235,200, used Tillotson ML5B
Model J - SN 235,201 - 235,999, used Carter N703S & N704S
Model J - SN 236,000 - 237,000, used Tillotson ML5B
Model J - SN 237,001 - up, used Carter N703S & N704S