1965 Carter 1 1/4" BBD Carb. 1 barrel question

1965 Carter 1 1/4" BBD Carb. 1 barrel question

I have a 1965 dodge dart 270 4-door now for sale on another thread, but I need some help with a carburetor question. The motor is the 225 c.id. and has the trusty 1bbl (BBD 1 1/4") Carter (carb. #383836 I think). SEE ATTACHED PICTURE. ARROW POINTS TO HOLE.
The question is - when rebuilt the carb I noticed a small hole ~0.125" or smaller drilled into the lower portion of the carb. I can see a similar hole looking in the Mopar service manual but it is not described and almost looks plugged. At first I thought it was for propane insertion into the carb for emissions settings from the factory. The hole passes into the inner part of the carb. and theoretically would be a huge vacuum leak. I tested with a gauge at idle and also revving the motor to see if I could get a veturi type signal or just a plain vacuum signal, but nothing on either engine speed seems weird. Was this plugged from the factory? Can I leave it open? It is above the butterfly on the cast iron portion not in the aluminum. Any thoughts would be appreciated.