CARBURATEUR SOLEX 34 PBIC

For a more technical approach to adjusting the Carter carburetor on the Willys MB, let's dive into the detailed procedures that focus on the internal components, settings, and specific specifications required to achieve optimal fuel-air mixture for both idle and high-speed operation.

The Carter WO (also known as the Carter Model WO carburetor) was used in the Willys MB and Ford GPW military jeeps, and understanding the finer points of its adjustments is crucial for maintaining performance.

Carter Carburetor Adjustment Procedure (Technical)

1. Understanding the Carter WO Carburetor Design

The Carter WO carburetor is a single-barrel, downdraft carburetor with a vacuum-operated fuel metering system. It has an idle system, a main fuel system, and a high-speed circuit that together regulate the air-fuel mixture at different operating ranges.

The primary components involved in adjustments include:

• Idle Speed Screw

• Idle Mixture Screw

• High-Speed Mixture Screw

• Choke Mechanism

• Accelerator Pump

• Main Jet

2. Preliminary Checks

Before making any adjustments, perform the following checks:

• Fuel System Integrity: Check for fuel filter clogs and fuel line leaks. Ensure the fuel pump is providing adequate fuel pressure (3-4 PSI) to the carburetor.

• Carburetor Mounting: Ensure the carburetor is securely mounted to the intake manifold with no intake leaks. A vacuum leak can cause erratic idling or poor performance.

• Engine Compression: Check engine compression using a compression tester. Low compression can affect the carburetor's fuel-air mixture adjustments.

• Air Cleaner: Ensure the air cleaner is clean and properly installed. A dirty air cleaner can starve the carburetor of air, affecting the air-fuel ratio.

3. Adjusting the Idle Speed and Mixture

The idle speed and idle mixture adjustments are crucial for smooth engine idle and response.

Idle Speed Adjustment

1. Locate the Idle Speed Screw:

   • The idle speed screw is located on the throttle shaft lever of the carburetor. This screw adjusts the position of the throttle plate at idle speed.

2. Adjust Idle Speed:

   • Start the engine and let it reach operating temperature.

   • Using a tachometer (or listening for a smooth idle), adjust the idle speed screw to achieve a 600-700 RPM idle.

   • Clockwise increases idle speed, and counterclockwise decreases it.

3. Check Idle RPM:

   • Ensure the idle speed is steady. If the idle fluctuates or is too high, the carburetor may require further fine-tuning or cleaning.

Idle Mixture Adjustment

1. Locate the Idle Mixture Screw:

   • The idle mixture screw is located on the side of the carburetor, near the base. It controls the air-fuel mixture at low speeds and idle.

2. Adjust the Mixture:

   • With the engine at idle, slowly turn the idle mixture screw clockwise to lean the mixture (reduce fuel) or counterclockwise to enrich the mixture (increase fuel).

   • Optimal Adjustment:

     • Turn the screw slowly and wait a few seconds after each adjustment to let the engine stabilize.

     • The engine should run smoothly with no stalling or hesitation.

3. Fine-Tuning:

   • If the idle mixture is too lean, you may notice backfiring or rough idle. If too rich, the engine may exhibit black smoke from the exhaust.

   • Adjust for the best smoothness, which generally occurs when the screw is turned about 1-1.5 turns out from fully closed.

4. Adjusting the High-Speed Mixture

The high-speed mixture screw adjusts the fuel mixture at higher RPMs (above idle).

1. Locate the High-Speed Mixture Screw:

   • This screw is located near the air horn of the carburetor, on the side or front of the carburetor body. It regulates the mixture for mid-range to full throttle.

2. Adjust the High-Speed Mixture:

   • With the engine running at a higher RPM (such as 1500-2000 RPM), turn the high-speed mixture screw.

     • Clockwise for a leaner mixture (less fuel).

     • Counterclockwise for a richer mixture (more fuel).

3. Test for Smoothness:

   • A properly adjusted high-speed mixture will eliminate hesitations or surging. The engine should accelerate smoothly without stumbling or black smoke.

4. Fine-Tuning:

   • During testing, if you notice the engine stutters or has a flat spot under acceleration, it is likely too lean. If it runs rich, you’ll see excessive exhaust smoke and poor fuel economy.

5. Choke Adjustment

The automatic choke enriches the fuel mixture when the engine is cold to help it start more easily.

1. Check Choke Operation:

   • With the engine off and cold, the choke plate should be completely closed.

   • Start the engine and let it run. The choke plate should gradually open as the engine warms up.

2. Adjust Choke:

   • If the choke plate does not fully open when the engine reaches operating temperature, you will need to adjust the choke spring.

   • The choke spring is located on the choke shaft and controls the choke plate. Adjust the spring tension to ensure the plate opens fully once the engine reaches operating temperature.

6. Accelerator Pump Adjustment

The accelerator pump provides additional fuel during quick throttle openings.

1. Check Accelerator Pump Operation:

   • Manually press the throttle lever and watch for fuel squirting into the carburetor throat. If no fuel is present, the pump may be faulty.

2. Adjust the Accelerator Pump:

   • The accelerator pump linkage should provide a strong squirt of fuel when the throttle is depressed quickly.

   • Adjust the pump linkage for correct squirt timing and quantity. A slight delay in fuel delivery can cause hesitation, while excessive squirt can cause flooding.

7. Main Fuel Jets Adjustment (if applicable)

If the Carter carburetor has interchangeable main fuel jets, it’s essential to ensure the correct size is used for optimal engine performance.

1. Inspect the Main Jets:

   • The main jets are typically located under the air horn. If you need to replace them, ensure they are the correct size for the Willys MB specifications.

2. Adjust for Proper Performance:

   • Smaller jets will lean out the mixture, while larger jets will enrich the mixture. Use the correct jet size to avoid poor fuel economy or power loss.

8. Final Test and Fine-Tuning

1. Test Drive the Vehicle:

   • After all adjustments are made, take the vehicle for a test drive. Ensure the vehicle accelerates smoothly and idles evenly.

2. Recheck Settings:

   • After a few miles of driving, recheck the idle speed, idle mixture, and high-speed mixture. Fine-tune if necessary for optimal engine performance.

Common Adjustment Issues & Troubleshooting