Those ports on the head were for an A I R system ...air injection reaction.
Some had the AIR and some didnt.
Did your have it originally?
My 90 didnt , the replacement engine had the ports and came with a box of plugs for the holes in the head. Mine was EFI , so they were plugged.
If anything, having the AIR inactive or blocked as you described would send a richer signal to the Controller (ECM) making it run to a leaner setting.
Your rich problem is most likely the carb.
Dont neglect getting the system scanned with an OBD 1 scanner, or pull codes manually . If the TPS is shorted, or it has a MAP sensor problem, those can richen the mixture excessively also.
Is the check engine light on?
Fact is stranger than Fiction