Needle Seat Operation:
Located In a carburetor, the seat is usually a brass plug with a specially shaped tapered hole that accommodates the needle (a suspended brass pintle with a pointed rubber/Teflon end). When the needle is in the seat, fuel can't enter the float bowl. When the float (in the float bowl) drops below a set height, the needle lifts off the seat allowing fuel to enter the float bowl. The rising fuel level lifts the float, exerting pressure and closing the need assembly.