solex 32/24 pdsit 3 mystery port?

[Tortoise]

I am servicing my solex 32-34 pdsit carbs, because there was a high HC reading at the MOT emissions. I am confused about a port in the right hand side of the right hand carb. It is in the same position as the vacuum retard port on the left-hand side of the left hand carb (ie mirroring its position) and these are both on the opposite side and approximate position as the venturi set screws- i.e. in the main body of the carb. The port goes in, then turns down through 90 degees to the throttle butterfly plate, just as the vacuum retard port does on the left hand carb. The van "seems" to run OK, but has proved difficult to tune properly, (as per all the published tuning instructions), hence the rebuild..... but this mystery port does not seem to appear in anything I have read or can find on the internet. I did not notice this port whilst the carbs were fitted and running, but presume it must have been sucking air, as it would on the left hand carb. I assume it should be plugged? Any information would be really appreciated.
My van is fitted with a CU engine with a 009 distributor ie no vac adv/retard, so the left hand carb vac retard port has been plugged.
Thanks, Mike

[bigherb]

I assume it should be plugged?

Yep

[Tortoise]

Thank you bigherb!