Well, after 6 months, I finally get to put this topic to rest.

I'm happy to report back that I've resolved the issue above. I stupidly though that the carb vent tube from the top T connector was a drain tube and replace it with a long 2 feet hose and routed it to the back of the bike. The extra length of the hose and routing was restricting air flow and not allowing the carbs to breath. With the vent tube restricted, fuel from the gas tank wasn't properly flowing into the carbs and not filling the bowls after long draws on the throttle.