holley vacuum plug??

[deathcharger71]

on the front of my holley carb is a plug that was not plugged when i got it tuned and dialed it, i thought it was a mistake so i plugged it...but it ran worse. what the heck is the thing? is it supposed to be plugged or not? its on the front of the carb towards the passenger side.

[Chryco Psycho]

should be a manifold vacuum port & yes it should be capped , yuo rpm will drop & you will need to reset the mixture screws to correct for the vacuum leak