How the Carter WGD Carburetor Accelerator Pump Works (and Why the Leather Cup Matters)
The Carter WGD carburetor is a popular two-barrel carburetor used in many 1940s–1960s American vehicles. One of its most important components is the accelerator pump, which helps ensure smooth acceleration and engine response. Unique to the WGD is its leather-style accelerator pump cup, a design choice that offers superior performance under specific operating conditions. This article explains how the system works and why the leather pump cup is beneficial.
What Does the Accelerator Pump Do?
In a carbureted engine, when you press the gas pedal quickly, there’s a moment when extra fuel is needed before the main fuel delivery catches up. The accelerator pump fills this gap by injecting a quick burst of fuel into the carburetor's venturi as the throttle opens. This prevents the engine from stumbling or bogging down during acceleration.
How the Carter WGD Accelerator Pump Works – Step by Step
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Idle or Light Throttle:
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The pump cavity, located in the float bowl, fills with fuel.
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The leather accelerator pump cup sits at the top of the pump shaft, ready to be compressed.
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Throttle Opens Quickly:
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The throttle linkage pushes the accelerator pump shaft downward.
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The leather cup compresses and forces fuel through a check valve.
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Fuel Injection:
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Pressurized fuel travels through a dedicated discharge channel and exits through a small nozzle (squirter) into the carburetor throat.
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This instant fuel shot enriches the mixture just as more air enters, ensuring smooth engine response.
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Return Stroke:
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When the throttle returns to idle, the spring-loaded pump moves back up, and the cavity refills with fuel through a separate inlet check valve.
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Why the Carter WGD Uses a Leather Accelerator Pump Cup
One distinguishing feature of the Carter WGD carburetor is that it only uses a leather-style accelerator pump cup, unlike other designs that may offer rubber alternatives.
Benefits of the Leather Pump Cup:
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Fuel Compatibility: Leather is more resistant to ethanol-blended fuels than many early rubber compounds, reducing the risk of swelling or deterioration.
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Superior Sealing: When properly oiled or soaked before use, leather cups expand to form a tight seal inside the pump bore, ensuring strong and consistent fuel delivery.
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Durability in Storage: Leather retains its integrity over time if stored dry and properly maintained, making it ideal for classic vehicles that sit unused for long periods.
This design choice by Carter was intentional and remains an asset for reliable pump operation, especially in classic engine applications that demand consistent performance.
Common Accelerator Pump Issues in Carter WGD Carburetors
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Dry or cracked leather cup: May occur if the carburetor has sat unused or was stored dry.
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Weak pump stroke: Caused by a worn cup or linkage issue.
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Clogged discharge passage: Prevents fuel from exiting the pump system.
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Sticking check valve: Delays or restricts fuel flow into or out of the pump circuit.
Tip: Always apply a few drops of oil to the leather pump cup before installation to ensure optimal sealing and longevity.
Conclusion
The accelerator pump in the Carter WGD carburetor is essential for delivering a smooth, hesitation-free driving experience. Its unique leather cup design offers excellent fuel resistance, long-term durability, and superior performance under classic engine conditions. Understanding how this system works helps you properly maintain or rebuild your WGD carburetor for optimal operation.
