I just went out and checked out my Smoke Vault. There may not be an adjustment on the burner venturi tube unless you do a partial dis-assembly...not sure on that though. I can see the venturi inlet air screen section from underneath, but it is partially hidden inside the burner housing. I can't tell if there is any adjustment or not.
The screen must be kept clean in order for a proper mixture...if it gets too dirty/clogged with greasy dirt, spider webs, etc., there will be alot more yellow/orange present on the flame tips due to a rich fuel/air ratio.
As for the cook chamber lower intake vents, they won't have much effect on the burner itself.