Rebuilding a set of Keihin 7A carbs and noticed #1 carb - i.e. carb with choke lever - is missing one of those little brass vent disks. Not sure if I did it when blowing out passages with my air compressor or if it was missing all along. It's not the disk in the passage that goes to the air vent line. It's the one on the other side of the jets. Anybody know how critical this for carb / bike operation if I don't replace it? Anybody know a source for these disks? Can I buy them separate anyhere or do I need to scavange one from another carb body?