When you accelerate, the accelerator pump supplies extra fuel that the engine needs. However, when not accelerating, the engine vacuum must be prevented from drawing fuel from the float bowl. This is where the discharge check ball comes into play, sealing the passage with the help of the discharge ball retainer. If the check ball doesn’t seal properly, fuel can leak into the venturi.
To ensure a proper seal, gently tap the check ball, see #32 & 33. It's made of stainless steel, so it won’t get damaged, but be careful not to hit it too hard, as this could deform the seat it rests on.
Pressing the accelerator also activates the accelerator pump, a small mechanical piston within the carburetor. This pump injects an extra squirt of fuel into the primary barrels, ensuring there is no hesitation or lean condition as the throttle opens. This helps to eliminate any flat spots or lag in acceleration, providing a smooth and responsive throttle response.