Valve cover hose question

[siteunseen]

While adjusting my carbs that hose is open to the atmosphere.  Should I plug it or just leave it open?

Thanks in advance. 

[rossiz]

if you mean the large one that attaches to the back of the air filter housing, it's essentially always open to the atmosphere - just inside the line of the filter, which is irrelevant from a vacuum standpoint.

unlike the efi system, the carbs can't see any pressure/vacuum other than what runs through them or the intake manifolds/balance tube.

[siteunseen]

Thank you sir!

More questions to follow...