Umair Gaines
The Rochester QuadraJet uses an automatic choke system that is very good, if properly set up and adjusted. There are a few different ways to adjust the choke on a Quadrajet, depending on the make and model of your vehicle. One common method is to adjust the choke when the motor is dead cold so that it just barely fully closes. You can then move it back and forth several times until it hits that point consistently. You should also check that you are getting power to the choke and that the choke coil is operational. If your choke is not working at all, you can try loosening the screws around the edge of the black cover and rotating the piece until the butterfly closes almost all the way.
| Characteristics | Values |
|---|---|
| Choke style | Two styles: divorced choke systems and integral choke |
| Divorced choke systems | Used from 1967-1974 |
| Integral choke | Used from 1975-1981 (except for heavy-duty trucks) |
| Hot air choke | Used from 1975-1979 |
| Electric choke | Introduced in 1980 to replace the hot air system |
| Choke adjustment | Loosen screws, adjust choke assembly, and retighten screws |
| Choke coil | Should mate correctly with the choke coil lever inside the housing |
| Choke pulloff | Should retract when the vacuum hose is sucked on |
| Choke blade | Should be fully closed when cold |
| Choke heater spring | May need replacement if choke is not closing up enough |
| Choke rod | Should be checked for bends to ensure free movement |
| Choke linkage | Can be adjusted to achieve the desired distance between the choke blade and airhorn |
| Fast idle | May need adjustment to prevent flooding |
| Secondary choke pull off | Can cause hot start and fast idle issues |
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What You'll Learn
Adjusting the choke on a non-electronic Quadrajet
The Rochester Quadrajet uses an automatic choke system that, when properly set up and adjusted, works very well. The choke coil tang in the cover must correctly mate with and engage the choke coil lever inside the housing.
To adjust the choke on a non-electronic Quadrajet, start with the engine cold. With the cover attach screws loose, rotate the cover so that the choke blade is fully closed. If there is no scribe line, rotate the cover counter-clockwise until the choke blade is fully closed. Lightly tighten the cover attach screws to keep the cover in this position.
Next, remove the short piece of vacuum hose attaching the choke pulloff to the vacuum nipple on the carb. Attach a long (about 2') vacuum hose to the pulloff. Suck on the vacuum hose to retract the choke pulloff. If the pulloff does not retract, it must be replaced.
With the pulloff fully retracted, use your other hand to lightly push down on the forward lower edge of the choke blade to simulate the force of the air across the blade. This will open the choke slightly. At this point, measure the distance between the forward lower edge of the choke blade and the forward wall of the air horn. This distance should be ¼”. To adjust, bend the tang on the choke linkage where it contacts the choke pulloff rod.
Finally, re-attach the vacuum hose to the pulloff and the carb.
It is important to note that the choke rod must be able to operate freely and not come into contact with the sheet metal cover, otherwise, the choke will not work correctly.
Some other general tips for adjusting the choke on a non-electronic Quadrajet include:
- Converting a 1975-1979 hot air choke to an electric choke by using the 1980 electric choke cover and removing the hot air choke gasket.
- Adjusting the choke pull off on a non-OEM install by having someone else start the engine while you have your fingers on the choke blade to fine-tune the adjustment.
- Using a rubber cap on the hot air inlet port on the choke housing to avoid sucking dirty air into the housing.
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Converting a hot air choke to an electric choke
The Rochester QuadraJet uses an automatic choke system that is very good if properly set up and adjusted. There are two styles of choke systems used in the Quadrajet. The first style, used from 1967 to 1974, is called a "divorced choke system". The second style, used from 1975 to 1981, uses a "hot air" choke. From 1980 to 1981, an integral electric choke was used in place of the hot air system.
The hot air choke system pulls clean air from a nipple at the back of the carb air horn, which then passes through a steel tube and a heat exchanger in the manifold crossover. The air then travels back into a steel tube and enters the front of the choke housing on the carb. As the engine gets hot, the air in the tube gets hot, and the coil expands to open the choke.
The 1980 electric choke cover can be used to convert a 1975-1979 hot air choke to an electric choke. To do this conversion, you need to:
- Remove the hot air choke gasket. If you do not remove the cover gasket when using the electric choke cover, the electric choke will not have a ground, and it will not function.
- Install a rubber cap on the hot air inlet port on the choke housing to avoid sucking dirty air into the housing.
- Connect the single wire that connects to the choke housing cover. The cover contains an electrical heating element that heats up the coil and opens the choke.
- Block off vacuum ports and connect the 12v wire. You will need a 12v "key on" power source for the element. The element should have 12v power the entire time the key is in the "on" position.
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Adjusting the choke pull-off
The next step is to remove the vacuum hose attaching the choke pull-off to the vacuum nipple on the carb and replace it with a longer hose. Suck on the vacuum hose to retract the choke pull-off. If the pull-off does not retract, it may need to be replaced. With the pull-off fully retracted, use your other hand to apply light pressure to the forward lower edge of the choke blade, simulating the force of air across the blade. This will open the choke slightly.
At this point, you should measure the distance between the forward lower edge of the choke blade and the forward wall of the air horn, which should be approximately 1/4". You can use a 1/4" drill bit as a gauge to check this distance. To adjust, bend the tang on the choke linkage where it meets the choke pull-off rod. Finally, re-attach the vacuum hose to the pull-off and the carb.
It is important to note that the choke pull-off should be adjusted with the engine cold, so it just barely closes. You can move it back and forth until it reaches this point. Additionally, the choke blade should be fully closed when cold at start-up, and the vacuum pull-off should open approximately 1/4".
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Adjusting the choke coil
The choke coil is an important component of the Rochester QuadraJet's automatic choke system. Adjusting the choke coil involves fine-tuning the choke pull-off and ensuring the choke coil tang correctly mates with the choke coil lever. Here is a detailed guide on adjusting the choke coil:
Understanding the Choke Coil System:
The choke coil is responsible for opening and closing the choke, which regulates the air-fuel mixture entering the engine. The coil is heated either electrically or by hot air from the manifold crossover, causing it to expand and push a rod that opens the choke.
Ensure that the choke coil tang in the cover correctly engages with the choke coil lever inside the housing. This step is crucial for the proper functioning of the choke.
Setting the Choke Blade Position:
Adjust the choke blade so that it is just barely fully closed when the engine is cold. This can be done by loosening the screws around the choke cover and rotating it until the desired position is achieved. Be careful not to overtighten the screws, as this may affect the choke's operation.
Retracting the Choke Pulloff:
Disconnect the vacuum hose from the choke pulloff and suck on it to ensure it retracts smoothly. If the pulloff does not retract, it may need to be replaced.
Simulating Airflow and Measuring Distance:
With the pulloff retracted, apply light finger pressure on the choke rod and lightly push down on the forward lower edge of the choke blade to simulate airflow. At this point, measure the distance between the choke blade's forward lower edge and the air horn's forward wall, which should be approximately 1/4 inch.
Adjusting the Choke Linkage:
If the measured distance is not correct, adjust the choke linkage by bending the tang on the choke linkage where it contacts the choke pulloff rod. This will fine-tune the choke's opening and closing action.
Final Steps:
Reattach the vacuum hose to the pulloff and the carburettor. Ensure that the choke coil is operational and receiving power. Test the choke's performance during engine start-up, especially in cold weather conditions, and make any necessary adjustments.
Remember that adjusting the choke coil may involve some trial and error, and it is important to refer to the specific instructions provided with your carburettor kit or in the manual for your vehicle.
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Adjusting the choke on a cold engine
The Rochester QuadraJet uses an automatic choke system that is very good if properly set up and adjusted. Here is a step-by-step procedure for adjusting the choke on a cold engine:
First, ensure the choke coil tang in the cover correctly mates with and engages the choke coil lever inside the housing. With the cover attach screws loose, rotate the cover so that the indicator scribe line points straight up. This should fully close the choke. If there is no scribe line, rotate the cover counter-clockwise until the choke blade is fully closed. Lightly tighten the cover attach screws to keep the cover in this position.
Next, remove the short piece of vacuum hose attaching the choke pulloff to the vacuum nipple on the carb. Attach a long (approximately 2-foot) vacuum hose to the pulloff. Suck on the vacuum hose to retract the choke pulloff. If the pulloff does not retract, it must be replaced. With the pulloff fully retracted, use your other hand to lightly push down on the forward lower edge of the choke blade to simulate the force of the air across the blade.
Now, with the pulloff fully retracted and light finger pressure on the choke rod, use your other hand to lightly push down on the forward lower edge of the choke blade to simulate the force of the air across the blade. This will open the choke slightly. At this point, measure the distance between the forward lower edge of the choke blade and the forward wall of the air horn. This distance should be ¼”. You can use a ¼” drill bit as a simple gauge to check it. To adjust, bend the tang on the choke linkage where it contacts the choke pulloff rod.
Finally, re-attach the vacuum hose to the pulloff and the carb. It is important to note that getting the adjustment right on a stock application requires following the instructions that come with the carb kit or manual. Additionally, when adjusting the choke pull-off, it is helpful to have someone else start the engine while you have your fingers on the choke blade to fine-tune the adjustment.
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Frequently asked questions
First, make sure the choke coil tang in the cover correctly mates with and engages the choke coil lever inside the housing. Then, with the cover attach screws loose, rotate the cover so that the indicator scribe line points straight up, which should fully close the choke.
If there is no scribe line (electric chokes do not have lines), rotate the cover counterclockwise until the choke blade is fully closed. Lightly snug the cover attach screws to keep the cover in this position.
The choke blade needs to be fully closed when cold and at start-up, the vacuum pull-off needs to open approximately 1/4".
Loosen the three screws around the edge of the black cover on the passenger side of the carb. Use a piece of wire to hold the throttle open just a little bit. Now, rotate the black piece until the butterfly closes almost all the way.
Disconnect the divorced choke rod from the lever on the passenger side of the carb.
