What are the Air Tubes - also known as Air Joints?
Of the two sets of plastic tubes between the carbs, the air tubes are closest to the aluminum plenum (the part below the air filter).
On '82 models and some early '83 models, the two air tubes routed into the aluminum plenum. But then Honda found that the air pulses through the airbox were affecting the float bowl levels. So they tied the two air hoses together under the plenum and created an additional nipple at the rear of the rack to attach the "J" hose to vent the carbs to atmosphere - independent of the airbox plenum. The "J" shape of the hose is to keep debris out of the Air Tube.
Note: If the air tube is plugged, the flow bowls cannot receive any gas than what is already in the float bowl and the bike will quickly stall.
Here is a picture of a V65 Sabre carb rack that shows the Air Tube - missing the "J" hose. -orange rectangle You can also see one end of the hose that connects the two tubes together under the plenum. -blue rectangle (this pic also has the location of the carb springs circled)
And here is a picture of a V65 Magna plenum with the holes so that - when oriented correctly - the air tubes poke through the plenum. As you can see in this pic, the brass colored plate to cover the rear hole is missing.