It is the right side vent on the petcock that goes to the right side carb. Hard to really get a clear pic. This is a brand new petcock. Not sure if the popping sound when I let of the gas at higher RPM's is associated with it, but I have a feeling it is an excess fuel problem. Bike runs very strong and has no idle nor high RPM issues other rhan this.
That doesn't sound right, but it's real hard to see where all the lines run. Normally, the center port of the petcock (vacuum port) runs to the left carb. Then each side port (fuel) runs to each carb fuel inlet.
In stock form, a vent hose comes off each carb, into a tee, then a single vent
line runs to the right side air filter box.
Then as described, the right carb has a vacuum
line that runs to the emissions valve under the seat.
Left/right is identified as you are sitting on the bike, versus standing in front.
Now, it is possible to connect the petcock vacuum to the right side carb, it would make no difference, except a lot longer hoses would be needed.
Can you describe again where the fuel is coming from? If it's the right hand port of the petcock as you look at it from the side of the bike, that is a fuel
port and may be loose and leaking as your old one was. Not sure right now.
The pop on decel is more than likely from a lean condition at idle. There are "coast enrichers" on the carbs that can stick, and the emissions system can play a part in causing decel pop also. Removing emissions and adjusting air screws can help. See: "coasters" on the site, also called "coastering", I think.. Mine still popped after coasters were done, but a few rides with seafoam and popping stopped (stuck coast enrichers).