Feufeu, the smaller american threads (under 1/4") are numbered. 10-32, while not exact may be represented as 3/16" UNF.
If the screw is stripped sometimes adding a washer will get it onto a working part of the thread. if the hole is stripped it might be possible to tap m5 and use an m5 screw. If you have a 94 carb the top screws are 10-32 unf.
Mart.