Hi Luke,
those yellow plastic tubes are the fuel feed. The single tube comes down from the gas tap on the aftermarket gas tank, the blob in the middle is an in-line gas filter and the plastic Tee splits the gas flow into two, one tube to each carb's gas connection.
Looking just below the in-line gas filter you'll see a small black rubber cap that's blocking off a metal tube that's sticking out of the carb-to-engine adapter piece.
That's the vacuum connection. There's another one on the other carb's adapter.
They were used on the stock bike to work the vacuum operated stock gas taps that your bike don't have any more.
They are blocked off so the engine can't suck in extra air through them and screw up the fuel mixture.
Their other use is for hooking up vacuum gauges when balancing the carbs.