HOW IT WORKS

Upon acceleration, the air flow through the carburetor responds almost immediately to the increased throttle opening. There is, however, a brief interval before the flowing fuel, which is heavier than air, can gain the required flow speed to maintain the desired balance of air and fuel. During this interval, the accelerator system supplies fuel until the other systems can one again provide the proper mixture. When the throttle is closed, the diaphragm return spring forces the diaphragm toward the cover, drawing fuel into the chamber through the inlet.

The inlet has an elastomer valve (aka umbrella check valve) which uncovers the inlet hole to admit fuel from the fuel bowl. The valve covers the inlet hole when the accelerator pump is operated to prevent the fuel from returning to the bowl. A discharge weight and ball check prevents air from entering from the discharge nozzle when fuel is drawn into the diaphragm chamber. When the throttle is opened, the diaphragm rod is forced inward, forcing fuel from the chamber into the discharge passage.

Fuel, under pressure, forces the pump discharge weight and ball off their seat, and fuel passes through the accelerator pump discharge screw and is sprayed into each main venturi through discharge ports. An air bleed in the wall of the accelerator pump fuel chamber prevents vapor entrapment and pressure build-up in the diaphragm chamber.

The accelerator pump circuit in the Motorcraft 2100 carburetor is designed to provide a momentary extra shot of fuel when the throttle is suddenly opened. This helps prevent a hesitation or "bog" when you step on the gas pedal. Here's a breakdown of how this circuit works:

1. Accelerator Pump Diaphragm:

   • The heart of this circuit is the accelerator pump diaphragm, usually located on the side of the carburetor. This diaphragm is directly linked to the throttle linkage. When you press on the gas pedal and open the throttle, this linkage pushes down on the diaphragm.

2. Fuel Reservoir:

   • Beneath the diaphragm is a small fuel reservoir. As the diaphragm is pressed down, it forces fuel out of this reservoir.

3. Nozzle (or "Squirters"):

   • The fuel forced out by the accelerator pump travels through a passage and is then squirted into the primary venturis via the accelerator pump nozzles, sometimes known as "squirters". This provides a richer mixture, giving the engine that extra burst of fuel needed when the throttle is opened rapidly.

4. Refill:

   • Once the throttle is released, the accelerator pump diaphragm is allowed to return to its original position. During this time, the fuel reservoir refills in preparation for the next throttle opening. There's usually a one-way check valve in the circuit to ensure fuel flows into the reservoir without being pushed back into the main float bowl.

5. Adjustment:

   • The amount of fuel squirted and the duration can often be adjusted, either by changing the position of the linkage on the diaphragm arm, swapping out the nozzles for ones with different sizes, or changing the cam that operates the pump linkage. This adjustment ensures that the right amount of fuel is provided during acceleration, based on the engine's specific needs.
   • Refer to our specifications sheet for adjustment data.

   https://youtu.be/Ac2tgqfFU28

PRE 1964 2100 PUMP

2100 carbs manufactured before 1964 do not use the umbrella check valve. Instead:

A- Fuel enters here from the float bowl.

B- Check ball drops down this hole to block off the fuel. The suction from the pump returning and the weight of the fuel raises this check ball and allows fuel to enter the accelerator pump cavity.

C- This screw is used to stop the check ball from floating out of the hole.

DISCHARGE

This check weight (#8) is used in the main discharge of some 2100 carbs. Under the venturi you place the check ball (#9), and then the check weight. The check weight is used to hold the check ball when the engine is not accelerating. Without it, the check ball would float up and allow fuel to be siphoned out.

When accelerating, the fuel pressure will lift the check ball and check weight to allow fuel to flow into the venturi. The check ball is a 3/16” steel ball.

The check weight can be purchased here. This check weight must fit into the venturi screw. If the diameter of the hole in the venturi screw (#6) is smaller than the diameter of the check weight (.11”), your 2100 carb does not use a check weight.

2100 discharge check weight

TROUBLESHOOTING

POTENTIAL ISSUES

If the accelerator pump circuit isn't functioning properly, the most common symptom is a hesitation or "bog" during acceleration.

• Over time, the diaphragm can wear out or develop cracks, leading to reduced performance or even fuel leaks. This can often be diagnosed by fuel leaking from the relief hole.
• Clogged passages or nozzles can also hamper the circuit's performance. Regular maintenance and cleaning can help prevent such issues.