Setting Ignition Timing
Setting your ignition timing is very easy, and important to do. Proper timing will not only yield better performance and emissions; it will also extend the life of your engine. To adjust the engine's ignition timing, you simply loosen the hold down bolt at the base of the distributor and rotate the distributor in very small increments. I am going to concentrate this "how-to" on setting the optimum timing. I am also going to assume that the timing is already close. That means the engine will start-up and run at least.
I call this method of adjustment, "Timing by ear", because you literally set the timing by sound. Itís not as hard as it sounds (no pun intended). Automotive manufactures do supply ignition timing setting for every application. You could simply use a timing light, and set the engine to that setting. There are several reasons not to do this. First, if your engine is not stock, the spec doesn't apply. Second, the timing marks on harmonic balancers aren't always known for their accuracy. Third, and (I think) most importantly, the factory spec is for sea level. At higher altitudes, more initial advance is usually required to ignite the thinner air fuel mixture.
The first step is figuring out which direction to rotate the distributor to advance the timing, and the direction to turn to retard it. Locate the vacuum advance module, and note the direction that it is attached to the distributor body. Look at the following picture to understand this. To remember this, recall that when vacuum is applied to the module, it pulls on the timing plate inside the distributor to advance the timing. You need to rotate the distributor in the same direction to advance the timing.
First, the engine must be warmed up to normal operating temperature. Then remove the vacuum advance hose from the distributor and plug the hose. If the engine runs fine with no surging or pinging, you can advance the timing. With the engine off, advance the distributor a couple of degrees. Start the engine. If it starts fine, shut it off and advance the timing a couple more degrees and restart the engine. When the starter/engine lugs or struggles when starting, you have gone too far. Backup the timing just enough, so that the starter spins the engine easily again. Tighten the hold down bolt and reattach the vacuum hose.
Now take the car for a test drive. Drive at several different speeds, and accelerate hard once or twice. If any pinging is heard, retard the timing a little more. Also, try driving steady at about 40-50 mph at part throttle. If any slight surging in the engine is noted, retard the timing a little.
You now have optimal ignition timing. You may want to use a timing light to see where the timing is now at just for future reference. Realize that if you drive through a significant change in altitude, you may need to slightly adjust your timing.