How it’s works? Pump system of Old cars carburetor.
When the throttle is opened rapidly, the air flow and manifold vacuum change almost instantly.
Because of the great difference in weight between air and fuel, any sudden change in throttle opening results in an immediate increase in air intake, but the fuel, having greater weight tends to lag behind.
The result of this is momentary leanness.
Sudden leanness would cause the car to balk or jerk, or suddenly loose power. You don’t want this to happen. When you tramp the throttle pedal very quickly, you do it for a reason you want a quick surge of power.
This is actually what does happen. You know that the car doesn’t momentarily slow down (if it’s operating properly).
So let’s look and see what enables the carburetor to provide a proper air/fuel mixture when the throttle plate is suddenly opened and you get the required surge of cower.
The accelerator pump, located in the carburetor float bowl, provides the extra fuel necessary to overcome the leanness of the fuel/ air mixture and give smooth operation on all throttle openings.
This is accomplished by discharging extra fuel into the venture air stream whenever the throttle valve is opened quickly.
The pump system utilizes a pump plunger that is linked to the throttle lever by mechanical linkage. Any opening of the throttle valve causes the pump plunger to move downwards in the pump well.
This action forces fuel through the pump passages and out the pump jets into the incoming air stream.
As the throttle is closed, the pump plunger is lifted up in the well, creating a low pressure below the plunger.
An inlet ball check is lifted off its seat and allows fuel to flow into the pump well. At the same time, a discharge ball check seats to prevent air from leaking into the discharge passage.
A duration spring and return spring work together to give a controlled, smooth discharge for a moment after the accelerator pedal stops moving.
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Article Source : This article courtesy should goes to Auto Mechanics Autodology – Technical instruction manual by System Operation Support.