Probably something to do with the automatic choke... probably to draw hot air thru the choke.
Check to see if there is a vacuum present at the port..
Does the car run ok without it? If so try putting a cap on it and see if it passes smog.
If not investigate farther.
I just moved from so cal and passing usually depends on whether you get a friendly tech. Just be polite and maybe talk about classic cars...
Also.. is the carb 5he factory one.. 5here are a lot of different models..
If the tech questions yiu about the plugged port.. tell him it was that way when you bought it.
Good luck