Carter WO Accelerator Pump

To adjust the pump throw on a Carter WO carburetor, follow these steps to ensure proper accelerator pump operation:

 Tools Needed:

• Small ruler or caliper

• Flathead screwdriver

• Carburetor specification sheet (for exact measurements)

Adjustment Procedure:

• Remove the Top Cover (Air Horn):
  Remove the carburetor from the engine if needed, and take off the air horn to access the pump mechanism.

• Locate the Accelerator Pump and Linkage:
  The pump sits in a vertical well and is connected to a small linkage arm that rides on the throttle shaft cam.

• Measure Pump Height (Plunger Setting):
  With the throttle in the closed position, measure the distance from the top of the pump stem to the top edge of the carburetor body.

• Measure Pump Height:
  With the throttle in the wide open position, measure the distance from the top of the pump stem to the top edge of the carburetor body.
  
  The difference between the 2 measurements should be 17/64".

• Adjust the Pump Linkage:
  Bend the linkage rod slightly to raise or lower the pump stem height as needed. Put the bottom of the rod in a vise up to the 1st bent.

  • More throw increases fuel delivery.

  • Less throw reduces it.
    Only make small adjustments to avoid over-fueling or bogging.

• Check for Smooth Movement:
  Open and close the throttle by hand and ensure the pump moves smoothly and squirts fuel cleanly into the bore.

• Reassemble and Test:
  Reinstall the air horn and test the throttle response. If there’s hesitation or a bog, fine-tune the linkage again.

Tips:

• Make sure the pump well is clean and the leather or rubber cup is in good shape.

• Use fresh fuel-resistant grease if necessary to lubricate the pump cup.

Test The Accelerator Pump Circuit

• Remove the tower. This gives you access to the float bowl.
• Fill float bowl with fluid. We use mineral spirits.
• Using the accelerator pump press down into the pump well.
• You should get a strong squirt out of the main discharge tube inside the carb throat.
• What to do if you don't get a good squirt?
  Remove the main discharge jet and clean. Check for a plugged passage
  A hard to remove jet can be removed by applying heat to the outside of the jet housing.
  Squirt carb cleaner into the hole (discharge jet) that leads to the pump well. It should go clear through.
  
  

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  You may be having accelerator pump problems on a Carter WO carburetor if you notice the following symptoms:

   Common Signs of a Failing Accelerator Pump:

  1. Engine Hesitation or Stumble
     When you quickly press the gas pedal, the engine hesitates, bogs down, or stumbles instead of accelerating smoothly. This is often the first and most obvious sign.

  2. Flat Spot on Acceleration
     There’s a noticeable “dead zone” or lag when you begin to accelerate from idle or low RPM, especially under load.

  3. Backfiring Through the Carburetor
     A lean condition caused by lack of fuel delivery during acceleration can cause a backfire through the carb throat.

  4. Poor Cold Driveability
     The engine may be sluggish or hard to drive until it's fully warmed up because the pump isn’t providing the extra fuel needed for cold starts.

  5. No Fuel Squirt When Throttle is Opened
     Remove the air cleaner and look inside the carburetor while moving the throttle by hand. You should see a squirt of fuel from the discharge nozzle. If not, the accelerator pump isn’t working.

  6. Fuel Leaks or Gummy Pump Plunger
     A worn leather plunger, dry or cracked pump seal, or ethanol-damaged components may prevent the pump from sealing and delivering fuel.

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   Fix:

  A failing accelerator pump usually means the pump plunger is worn or dried out. Rebuilding the carburetor or replacing the pump cup (often leather on the Carter WO) will usually resolve the issue.

  If you need parts or a rebuild kit, make sure they are ethanol-resistant and made specifically for the Carter WO model.

WO Discharge Jet