CAT Products offers an excellent...
CAT Products offers an excellent tool to administer a carbon removal chemical into the engine while running via a vacuum hose. It is very effective at removing IVD.
A good rule for any engine is that at very minimal throttle opening (idle) the burn rate is slower, so more advance is required. This is due to the lack of turbulent motion in the bore as the piston sweeps toward TDC. It is the result of a minimal amount of volumetric efficiency (cylinder fill percentage) due to the slow piston speed and the throttling effect of a closed throttle plate. As the throttle is opened more, the volumetric efficiency improves along with the burn rate. As with many things in an engine, the spark advance rate is usually an inverted bell curve.
The problem with altering the base timing at idle for a slow speed means that you are skewing the total spark advance curve. For this reason, it will be necessary to recurve the distributor to achieve the same total timing at a given engine speed and load, while satisfying the requirements of the engine at idle. You cannot just twist the distributor and forget about it.
Many Pontiac engines had an...
Many Pontiac engines had an adjustable idle-up solenoid that would evoke when the A/C was engaged to increase the engine speed. This allowed for a slow idle and a means to compensate for the load of the compressor.
With the basics established, we will now discuss how to go about lowering the idle speed on your Pontiac.
A manual transmission Pontiac will always be able to idle at a slightly lower speed than one with an automatic transmission due to the load the torque converter places on the engine when in a drive gear. A very loose drag race-style converter will slip at idle and not load the engine but will be inefficient and drive poorly on the street. For this reason, our discussion will be focused on the stock or street/strip Pontiac and not a race engine.
The first place to go when attempting to lower the idle speed is the basic tune-up. The Pontiac should not be suffering from a dirty carburetor, fouled spark plugs, a plugged air filter, and a multitude of vacuum leaks. You need to make sure that the engine and its sub-systems are in proper working order.
A Holley carburetor has a...
A Holley carburetor has a booster style in the venturi that was designed more for performance than idle quality and low speed operation. It works well but was not as precise as a Rochester carburetor in these areas.
With this accomplished, the next step is to adjust the idle mixture screws for the proper air/fuel ratio. This is very easy but requires patience, along with a tune-up style tachometer for precise resolution.
To properly adjust the mixture screws on any Pontiac, follow these steps:
1. With the engine off, gently seat the mixture screw(s) and then turn them out two complete revolutions.
2. Connect a tune-up tachometer and start the engine and allow it to fully warm-up.
3. With a helper sitting in the driver’s seat and his or her foot on the brake, the wheels chocked, and the parking brake on, place the transmission in drive.
The Quadrajet has the now...
The Quadrajet has the now famous booster within a booster design. It provides a very strong metering signal and excellent fuel atomization at low engine speeds. Superb engineering.
Adjust the idle speed screw to the slowest smooth idle that can be achieved.
5. Install the air filter and housing while locating a tool that will allow access to the mixture screws with these parts in place. You want to adjust the carburetor with the pressure drop created by the air cleaner.
6. Slowly turn one mixture screw in (lean) while watching the tune-up tach. Go in 1⁄64 of a turn and then wait for the engine to stabilize. Keep doing this until the engine speed drops. Then stop.
The mixture screw in a performance...
The mixture screw in a performance carburetor is removed from the discharge point and is housed in the metering block. A design that works well but is not the best for a slow, smooth idle.
Now incrementally turn the mixture screw out (rich) in 1⁄64 increments, waiting for the engine to stabilize while watching the tach. Be patient. Keep doing this until the highest engine speed is obtained. Then repeat the procedure for the other mixture screw.