Did you put the diaphragm gasket on correct ?
Been 'many'' years since I rebuilt one of those,, but do remember that it's very important in having the diaphragm gasket on ''I believe'' the cover side.
Not 100% on that , but seem to remember them being that way ...
Course, I've done ''a lot'' of different types of diaphragm carbs over the years ….
Pretty much forgot more than most people will ever learn about mechanical stuff ect. though..
LOL