66 straight 6 exhaust manifold question

I am replacing the exahaust manifold gasket on my 1966 6 cyl. I bought a new choke tube that goes from the top hole in the manifold to the carb. There is another hole on the bottom of the manifold beneath the choke tube hole that has a brass fitting in it. What is this for? Should I just plug this hole? There was no tube in it when I bought the car a year ago and it runs great, just needed another exhaust manifold gasket.  

That lets the air in so it can travel up the choke tube.  
Bill

1966 coupe
1995 Cobra R

Thanks