That's the CNS V.1 carb. The tube you have a screw in goes from the bottom of the float bowl to the barbed vent on top of the carb. This is the fuel enrichenment circuit for the choke. Turning on the choke draws extra fuel through the circuit. Without that tube it doesn't get fuel. The 2 vent tubes side by side are vent tubes. They're ok just the way you have them.
Other than that it's a fine build