I have a Street Dominator intake manifold on my 350 motor.
There is a small vacuum port behind the carb. Well strange as it seem the motor semms to run a little better with the vacuum port open.
Should all vacuum ports if not used be pluged or can they be left open.
Seems to me you would loose some vacuum with it open, but the car at least idles better with the port open. Barb.

 

Sorry Barb, those ports need to be plugged. It seems to run better, but believe me it does not.

 

Eric, if it idles better with it open would that indicate the carb is too small? Or maybe not too small, but that it would benefit from a larger one? IDK...just wondering myself

 

When my timing chain skipped 30 degrees, my 350 block ran smoother when the #8 spark plug was unplugged.

THAT was weird..

 

I would say it indicates her tune may be a little off. It's probably adjusted to compensate for the vacuum leak.