As the accelerator pump moves up in the pump bore, gas fills the pump well through a slot on the side of the well. Fuel then flows down the well past the rubber cup.
When the accelerator pump is pushed down (accelerating), gas is forced out the main discharge passage and out the pump jet. The pressure of the gas forces the discharge check ball to raise up allowing fuel to move along.
When not accelerating, the discharge check ball is seated not allowing fuel to be siphoned into the carburetor bore. If you see gas dribbling out the discharge jet at idle, then it possible the check ball isn’t seated.
Seat the check ball by tapping on it lightly.
If the check ball is stuck in the hole, heat the outside of the carburetor where the check ball resides and turning the carburetor upside down, tap the carburetor on your work bench. The check ball will fall out.
