If I'm reading it correctly...look inside the airscrew orifice with a tiny hooked pick, the o-ring may be lurking inside.
If the carbs are on the bike, verify that the float valve is not affected by gravity (i.e. dropping out) then move the float with your hand until it just touches the needle of the valve. Then measure from the float to the carb body, should be whatever the manual specs are, if not, bend the little tab on the float arm until it's correct.
Hope it helps.
-Tim