I have a 2gc and i'm wondering what this port is for because i know that the other is for fuel, but not this one. i have been told it was a vacuum port.
That is the fuel bowl vent tube. Some attached to the air cleaner and some to attached early emissions. You can leave it open...Don't plug it
To avoid any chance of a stick float dumping fuel on the engine, run a short length of hose into a dump tube that gets the fiel away from the engine. To avoid effecting carb calibration the dump tube should be substantially bigger than the short hose connected to the fitting.
The Jalopy Journal
