Carter WCFB 4 Barrel Carburetor Choke

How the WCFB Choke Works

WCFB Choke Parts

Choke Hot Air Vacuum Passage

The thermostat is twisted either clockwise or counter clockwise in order to close the choke valve. Disregard any index marks. Your thermostat may be a retrofit and after some many years the carburetor is worn past being new.

Hot air comes form the manifold through the hot air pipe into the choke housing. This is pulled by vacuum coming through the choke housing. As the choke coil is heated up it looses its tension allowing the choke valve to open.

The choke valve opens on it's own. Using the engine vacuum to pull it open and the weight of the choke linkage pulls it open.

WCFB Linkage at Curb Idle

Notice where the fast idle cam is at idle. With all choke adjustment it might be on the lowest cam spot.

Notice where the fast idle cam when on fast idle. The spring is what brings the fast idle cam back to starting position.

Hard Starting?

If your Carter WCFB carburetor is experiencing hard starting, try this troubleshooting step:

Press on the gas pedal once. This action allows the fast idle cam to drop, while simultaneously squirting an extra amount of gas from the accelerator pump into the carburetor barrel.

If you do not observe this squirt of gas when the engine is cold, then you likely have an issue with the accelerator pump circuit.

Pump circuit problems:

The main discharge check ball may not be sealing.
The pump well isn't filling up with gas on the up stroke.
The fuel bowl is too low by possibly a weak fuel pump, or maybe the float setting being way off.
After turning off a hot engine the gas may be siphoning into the intake. Look down the carb after turning off to see if gas is dribbling out of the venturi.

Adjusting WCFB Electric Choke

Adjusting the electric choke on a Carter WCFB carburetor is a straightforward process, but it needs to be done carefully to ensure reliable cold starts and proper drivability. Here's how you do it:

Tools You’ll Need:

Flathead screwdriver
A wrench or socket (if needed to loosen the choke housing screws)
Optional: Timing light or tach for idle speed adjustments

Steps to Adjust the Electric Choke on a Carter WCFB:

1. Identify the Choke Housing

The electric choke housing is a round, usually black or metal disc on the passenger side of the carburetor.
It’s held in place by three screws and contains a bi-metal spring that controls the choke plate.

2. Cold Engine Test

Make sure the engine is cold, ideally after sitting overnight.
Remove the air cleaner so you can see the choke plate in the primary throat of the carburetor.

3. Observe Choke Plate Position

The choke plate should be just about fully closed when the engine is cold.
If it’s too open or too tight, adjustment is needed.

4. Loosen the Choke Housing Screws

Loosen (don’t remove) the three screws that hold the choke housing in place.
The housing is adjustable by rotation.

5. Rotate to Adjust

Turn the housing clockwise to make the choke richer (more closed when cold).
Turn counterclockwise to make it leaner (more open when cold).
Make small adjustments, about 1–2 notches at a time.
After adjusting, gently hold the throttle open and watch how the choke plate reacts. It should close firmly but not too tight.
NOTE: Clockwise & Counterclockwise might be backwards on some carburetors.

6. Tighten Screws

Once you’re satisfied with the choke plate’s cold position, tighten the three screws back down.

7. Check Fast Idle Cam Engagement

With the choke closed, the fast idle cam should be positioned to increase idle speed during cold starts.
Manually open the throttle to ensure the fast idle cam engages properly.

8. Warm-Up Test

Start the engine and observe:
- The choke plate should gradually open as the engine warms up (within a few minutes).
- Idle speed should drop as the fast idle cam releases.

Final Tips:

If the choke opens too slowly, it may run too rich and bog down.
If it opens too fast, the engine may stumble or stall when cold.
Make sure the electric wire going to the choke receives 12V with the key on (engine running or ignition on).
Use a tachometer to fine-tune idle and fast idle RPMs if necessary.

Carter WCFB Choke