The CNS is an old style Mikuni clone, it has 5 fuel metering circuits and requires a step by step method to tune properly. Its a trial and error process that requires patience and a good
understanding of the fuel circuits and their effect on the engine.
The hoses attached to it are air vents except for the top and bottom ones, the top one is a oil injection fitting that the chinese decided to attach to the fuel bowl overflow. This should show no fuel flow unless the float is set high. In a old school road bike or off road motorcycle application the bottom port is a hose run to the ground (overflow) and the top port is connected to the oil pump. The other two are plumbed to the clean side of the air box or fitted with tiny foam filters.
http://www.mikuni.com/pdf/vmmanual.pdf
The stock HT carb is easy to setup, their is only really 2 tune-up options, main jet and needle clip, Unless you start adjusting the slide cutaway or needle taper.
In a real carb like the CNS the fuel circuits overlap and must be tuned to work together. When setup properly the difference is awesome. Crisp idle, solid midrange and a cool running WOT.
Even better results can be gained from a real 16 to 19mm Mikuni or Delorto since the CNS is a crappy clone with loose tolerances.
New CNS owners should do the trial and error stuff on the stock carb, try different main jet sizes, clip positions, plug readings engine responce ect. then when confident move on to the more complicated setup.
Good things to know about using CNS or similar carbs.
The cable operated choke circiut has no effect on air flow and is a great tune up tool, a lean or rich setting can be verified by your handlebar mounted choke application.
4 stroking can happen when lean as well, bump the choke and see.
Air screw adjustments slightly affect the full RPM range so allow for weather/conditional running.
I have set up my CNS for lean idle, crisp midrange running and use the "choke" for extra fuel for high revs and hills.
"Fuel is the main coolant for two strokes". Gordon Jennings
These HT's love a rich WOT.