1967 Carburetors Without Cleaner Air Package
1967 CAP carburetors can be identified by a green tag on the air horn.
- Remove the air cleaner.
- Run the engine at fast idle to stabilize the engine temperature.
- Make sure that the choke plate is fully released.
- Connect a tachometer to the engine following the manufacturer's instructions.
- On models with 6 cylinder engines, turn the high beams on. If equipped with air conditioning, turn the air conditioner on. The transmission should be in Neutral, Park for automatic.
- Adjust the carburetor idle speed screw to obtain the specified idle speed.
- Turn the idle mixture screws in or out to obtain the highest possible rpm. After obtaining the highest rpm, turn each mixture screw clockwise until the rpm's start to drop. Then turn the screws counterclockwise just enough to regain the lost rpm.
- If the idle mixture adjustment has changed the idle speed, readjust the idle speed.
- Remove the tachometer and install the air cleaner.
- Remember to turn the lights off when you're finished.
Except 1967 Carburetors Without Cleaner Air Package
The CAS replaced the CAP in the 1968 model year. CAP carburetors are identified by a green tag attached to the carburetor air horn.
To adjust the idle speed and mixture on these carburetors, particularly on later models, it is best to use an exhaust gas analyzer. This will insure that the proper level of emissions is maintained. However, if you do not have an exhaust gas analyzer, use the following procedure and eliminate those steps which pertain to the exhaust gas analyzer. When you have adjusted the carburetor it would be wise to have it checked with an exhaust gas analyzer.
- Leave the air cleaner installed.
- Run the engine at fast idle speed to stabilize the engine temperature.
- Make sure the choke plate is fully released.
- Connect a tachometer to the engine, following the manufacturer's instructions.
- Connect an exhaust gas analyzer and insert the probe as far into the tailpipe as possible. On vehicles with dual exhaust, insert the probe into the left side pipe, since this is the side with the heat riser.
- Check the ignition timing and set it to specification if necessary.
- If equipped with air conditioning, turn the air conditioner off. On 6-cylinder engines, turn the high beam lights on.
- Put the transmission in Neutral, Park for automatic. Make sure the hot idle compensator valve is fully seated.
- If equipped with a distributor vacuum control valve, place a clamp on the line between the valve and the intake manifold.
- Turn the engine idle speed adjusting screw in or out to adjust the idle speed to specification. If the carburetor is equipped with an electric solenoid throttle positioner, turn the solenoid adjusting screw in or out to obtain the specified rpm.
- Adjust the curb idle speed screw until it just touches the stop on the carburetor body. Back the curb idle speed screw out 1 full turn.
- Turn each idle mixture adjustment screw 1 / 16 turn richer (counterclockwise). Wait 10 seconds and observe the reading on the exhaust gas analyzer. Continue this procedure until the meter indicates a definite increase in richness of the mixture.
This step is very important when using an exhaust gas analyzer. A carburetor that is set too lean will cause a false reading from the analyzer, indicating a rich mixture. Because of this, the carburetor must first be known to have a rich mixture to verify the reading on the analyzer.
- After verifying the reading on the meter, adjust the mixture screws to obtain an air/fuel ratio of 14.2:1. Turn the mixture screws clockwise (leaner) to raise the meter reading or counterclockwise (richer) to lower the meter reading.
On 1975-77 models, adjust to get the air/fuel ratio and percentage of CO indicated on the engine compartment sticker.
- If the idle speed changes as the mixture screws are adjusted, adjust the speed to specification (see Step 10) and readjust the mixture so that the specified air/fuel ratio is maintained at the specified idle speed.
If the idle is rough, the screws may be adjusted independently provided that the 14.2:1 air/fuel ratio is maintained.
- Remove the analyzer, the tachometer and the clamp on the vacuum line.