I have a .36NX, a .46NX and a .61NX, all without any problems at all. But, I recall that Evolution had some problems with sealing the carb. Try putting a new "0" ring between the carb and spigot, and try putting fuel line on the needle valve. Make sure everything is tight and leak free.

When it is running erratically, try squirting some fuel along the carb base and/or along the needle where it screws into the needle valve. If the running smooths out, you have an air leak at that point. Good luck.

Sincerely, Richard