Jaguar, are you refering to "southern engineer" as drilling & filling the jet?
Behr, the two top ports need the plastic tubes, they are air vents and just float in the breeze. If you have Grubee CNS then the bottom port is a overflow drain. I like to extend the tube downward by the kickstand and secure it with a ziptie. If you keep the drain tube short you will get fuel on your feet. If you have the non-Grubee CNS then the bottom port (the drain) is routed back to the carb and recycled to the engine (better choice).
From my experience, the stock NT carb works better. For some reason CNS carb act like they are running out of fuel (cutout) at speed. Keep in mind that the choke circuit is different than most carbs too. CNS carbs have extra jet that allows addition fuel for cold starts. Don't leave it open to long of you will flood your engine & foul the plug. It can be cracked open when hill climbing or when running flat out.
Adjustment screws: Grubee CNS have only the idle speed screw (in for higher idle, out of lower idle). The non-grubee CNS has an additional fuel mixture screw.
Hope this helps and Good Luck!