Just my $0.02 on this mod as well since I have done this mod as well. The T connector between the carbs must remain open (you can leave the hose on it but make sure it's open to atmosphere) because you will have fuel flowing up through the carb jets and into your airbox if you close it off. The pressure or 'head' (fluid dynamics term) from the fuel in the tank (higher elevation and potential energy) is more than the pressure exerted by the float bowls to stop the flow. This causes the fuel to flow past the bowls, fill up the carbs and then flow out of the jets. The atmospheric pressure lets the float bowls do their job and float up to stem the flow from the tank.
