Try this:

Loosen the carb, then push it down firmly and re-tighten it.

Or, as long as you're going to loosen it, just go ahead and take it off. Remove the needle valve and give it all a good cleaning. Blow in the NV seat to make sure there's no blockage, and when you put the carb back on, make sure it seats firmly (And that the "O" Ring is good).