Sounds like maybe your base gasket is leaking.....have you checked the torque on the cylinder head nuts? You may want to start a thread in trouble shooting on this one and further describe the issues.
No it is not a CNS carb
As for the leaks my cousins and the one I built for my wife had no leaks on the tank and minor leaks. I am getting bad oil build up on the motor between the clutch lever and clutch plate area right below the intake but the intake isn't leaking