How the Accelerator Pump Circuit Works
As the pump returns to it’s top position, the suction of the pump and the weight of the gas lifts the inlet check ball and fills the pump well. The inlet check ball is there so that it plugs the hole when pressing on the gas, otherwise the gas would return to the float bowl.
When the accelerator is pressed down, the pump pushes the inlet check ball onto it’s seat and pumps the gas through the discharge passage, lifts the pump discharge needle and gas is sent out the discharge nozzle and into the venturi.
When rebuilding test the pump circuit before installing on your vehicle.
Make sure the pump discharge needle is in place and holding. To test, fill the bowl with fluid (mineral spirits) and while holding the needle down gently pump the accelerator. Fuel should not leak around the needle. If it does, inspect the needle for damage. Seat the needle by hitting it gently with a brass drift punch.