340 Six Pack Carb part ID

The center carb will not fill the bowl with gas. Both outboard carbs are getting fuel. I can manually fill the bowl through the sight screw and is runs until the gas is gone, then stops. At first I thought the float was stuck so I took the carb apart and this part fell out of the bowl when I opened it. I don't recognize it and I don't know if it belongs in there. It is plastic, but I don't see anything like it in the rebuild kit or the diagram. the float moves freely so it's not the float. Ant ideas as to what it is and where it goes and what it does?

Looks like a bowl vent cover, originals were metal, some replacements are plastic.

This is an old picture. Gasket goes over it.

OK Thanks I see now where it goes

I would pull the needle seat assy, chances are some crap has gotten into the seat, perhaps fine rust particles, just enough to hold the seat closed and not allow the bowl to fill...seats either get stuck open allowing flood conditions or seized close causing fuel starvation

Thanks Yes I did that and the seat works well I think that is what originally happened. It was stuck shut. Readjusted the float and will also do a complete gasket change and insert a filter in the inlet

Did it originally have a filter in the inlet? I've seen some with no filter.