[johnbuckley]

Toms Endy's article is excellent.
For Zeniths 5/8 inch is the usual advised level of the fuel below the upper casting,usually when the top and midline solder seam of the float are parallel with the machined face of the upper casting, BUT the weight/displacement of floats varies a bit so the only way to be sure of correct fuel level is to use the glass jar method that Tom shows in his article. [this can be done with the carb on the car if LHD- difficult if RHD... I use a slice of old inner tube to hold the jar in place whilst checking] . You may need one, two or even three gaskets +/- half thickness gaskets between the valve and the casting as various valves vary in their height. A kit of shim gaskets can be bought from the usual suppliers.
later edit: YBlockhead in post #7 below is absoluetly right... the fuel gauge he shows is a very useful inexpensive kit for quickly checking fuel level.