I have Zeniths on my 66 911. During a carb clean i discovered a threaded hole next to Idle Jet / Air bleed? This is located only on the center barrel near top and is connected to a mini jet in the base of the center float bowl confirmed via carbcleaner / air ect. I see in photos of restored zeniths that this port has a screwed plug or jet i seem to be missing this on BOTH carbs. IF i need to reinstall i have no idea what is to be installed. The car did run but im baffled on this black carburetor art.

Thanks Chuck