The needle valve has the spring loaded tip. The seat is the screw in portion the needle "seats" in which controls the amount of fuel allowed in the bowl. If the needle doesn't seat properly to stop the flow, fuel runs out out the overflow tube and possibly into the engine causing more problems. As XL said, make sure your "seat" is in good shape or replace it. Also, the float height needs to be set at the proper level for that model of carb. One other thing to check is the overflow tube itself; look for cracks where meets the bottom of the bowl.

Tom

Sedillo, New Mexico USA