The Rochester Dualjet is a 2-barrel carburetor used in various General Motors vehicles from the 1960s through the 1980s. It is similar to the Rochester 2-barrel carburetor but features an additional "jet" or secondary barrel for improved performance. The choke system is an essential component of the Rochester Dualjet carburetor, responsible for regulating the air-fuel mixture when the engine is cold.

Choke System Components:

1. Choke plate: A butterfly valve located at the top of the carburetor's primary barrel, which controls the amount of air entering the engine when cold. When the engine is cold, the choke plate is closed, restricting air and creating a richer air-fuel mixture for easier starting and idling. As the engine warms up, the choke plate gradually opens, allowing more air to enter and leaning out the mixture.
2. Choke pull-off (Vacuum break): A vacuum-operated diaphragm device that helps open the choke plate slightly after the engine starts. This prevents the engine from running too rich when cold and reduces stalling, hesitation, and poor fuel economy.
3. Choke thermostat: A temperature-sensitive coil or bimetallic spring that controls the choke plate's position based on engine temperature. As the engine warms up, the thermostat expands, progressively opening the choke plate.
4. Fast idle cam: A mechanism connected to the choke system, which raises the idle speed when the choke is engaged. This ensures smooth running and prevents stalling during the warm-up period.

Choke System Operation:

When the engine is cold, the choke thermostat contracts, pulling the choke plate closed. The choke pull-off slightly opens the choke plate after the engine starts to prevent it from running too rich. As the engine warms up, the choke thermostat expands, progressively opening the choke plate and allowing more air to enter the carburetor. This results in a leaner air-fuel mixture, which is more appropriate for a warm engine. At the same time, the fast idle cam lowers the idle speed to the normal operating range.

Maintenance and Troubleshooting:

To maintain optimal performance and fuel efficiency, it's essential to regularly inspect and service the choke system on your Rochester Dualjet 2-barrel carburetor. Here are some common issues and their solutions:

1. Hard starting or poor idling when cold: This may be caused by a malfunctioning choke plate that isn't closing properly. Inspect the choke plate for debris or damage and ensure it moves freely. Clean and lubricate the choke plate shaft and linkage as necessary.

2. Stalling or hesitation during warm-up: This could be due to a faulty choke pull-off that isn't opening the choke plate slightly after the engine starts. Inspect the vacuum hose for cracks, leaks, or blockages, and test the choke pull-off diaphragm for proper operation.

   

3. High idle speed when warm: This might be caused by the fast idle cam not disengaging properly as the engine warms up. Inspect the fast idle cam and linkage for wear or damage, and clean or replace as needed.

4. Choke not opening fully when warm: Check the choke thermostat for proper operation. If the thermostat is damaged or not expanding as it should, replace it.

Always consult your vehicle's service manual for specific information related to your make and model, as procedures and adjustments may vary. By maintaining the choke system on your Rochester Dualjet 2-barrel carburetor, you can help ensure optimal performance and fuel efficiency for your vehicle.

Dualjet Secondary Choke Pull-Off

The secondary choke pull-off (also known as a vacuum break) is responsible for opening the secondary choke plate after the engine has started and is warming up. This is important because it helps prevent the engine from running too rich when cold, which can lead to stalling, hesitation, and poor fuel economy.

The secondary choke pull-off is a vacuum-operated diaphragm device that is connected to the secondary choke plate via a linkage. When the engine is started, vacuum is applied to the diaphragm, causing it to retract and pull the secondary choke plate open slightly. As the engine warms up and vacuum increases, the diaphragm retracts further, progressively opening the secondary choke plate.

If the secondary choke pull-off is not functioning correctly, it can cause issues with the carburetor's performance, such as hesitation during acceleration or stalling when cold. To diagnose and fix issues with the secondary choke pull-off, follow these steps:

1. Inspect the vacuum hose connected to the secondary choke pull-off for any cracks, leaks, or blockages. Replace or clean the hose as necessary.
2. Test the secondary choke pull-off diaphragm by applying vacuum using a hand-held vacuum pump. If the diaphragm does not hold vacuum or the secondary choke plate does not move, the pull-off may need to be replaced. Be sure to block the pulloff bleed hole.
3. Check the linkage between the secondary choke pull-off and the secondary choke plate. Ensure that it is not bent, damaged, or disconnected. Repair or replace the linkage if necessary.
4. Inspect the secondary choke plate for proper operation. With the engine off, the choke plate should be closed when cold and gradually open as the engine warms up. If it does not operate smoothly, clean and lubricate the choke plate shaft and linkage.
5. Adjust the secondary choke pull-off, if necessary. Some models may have an adjustment screw or require bending the linkage slightly to achieve the correct opening of the secondary choke plate. Consult your vehicle's service manual for specific adjustment procedures.