Not sure what this is called.

Raulduke

I have a plug over this on my Mazda b2200 Weber carb. I was wondering where I could find a new plug to cover this. Mine is dry rotting. I would just order a new one, but I’m not sure what it’s called.

MazdaMitch

It's just a bowl vent and it still vents out the top of the carb so you can plug it or not plug it it's not really going to matter.

On one of my trucks I have a small brass filter inlet and on one truck I have it plugged off using a cap just a vynil cap.