Pierburg 1bs carb what are the x2 rear ports for?

Hi, I've got a Pierburg 1bs carb fitted to my mk1 auto and there are x2 ports of the rear of the carb that are sucking air but not connected to anything.

Are they meant to be connected to something?

The reason I ask is because when cruising at 60mph there's a faint stumbling, if I accelerate it disappears immediately. I thought that this might be causing the issue

I have a pdf about this carb with vw connections on last page