Setting your Engine Timing
written by AMC EN member "mccastlej"
The tools you will need are timing light; and a 1/2" wrench to loosen the distributor clamp; engine degreaser to clean off the timing scale and damper; and white crayon.
You need to locate the tune up spec chart label in the engine compartment and see what it is supposed to be set too.
Down by the harmonic balancer there is a timing degree scale. You need to clean this off enough to see the numbers on it. Also there is a notch on the harmonic balancer. Clean this and mark it with some white marker, or crayon, or something close.
If you don't have a tachometer, you can get close but not exact with RPM. Disconnect the vacuum advance hose from the distributor and plug it with a nail or something.
With the ignition off you need to connect the pickup from the timing light to the number 1 spark plug wire. If you have a light with an inductive pickup, it just clamps on the outside of the wire. If you have a direct connection, it the wire will have something on the end that looks like a spring. If you have this connection, you connect it between the spark plug wire, and the spark plug on #1 cylinder. Connect the battery connectors from the timing light to the battery making sure you have the correct polarity. Make sure you timing light wires are not going to get in the way of the belts or the fan.
Disconnect two-wire connector (yellow and black wires) at electronic ignition module and short circuit the ignition module connector with a jumper wire. (This deactivates the electronic timing retard circuit).
Start your engine. The TSM states to engage your parking brake, and put your car in drive. I don't know many eagles that have good enough parking brakes to hold the car in drive while it's running at 1600 RPM? You might want to chain your car to a good tree, or a truck or something? Or better yet have a reliable helper to keep their foot on the brake.
You will want to adjust your idle temporarily to the RPM designated on the Tune up spec chart label or you can have a assistant keep it at the proper RPM. You will need to turn the timing light on, and point it at the timing marks. Your light will illuminate the harmonic balancer mark. It need to be aligned with the correct number on the timing degree scale. If it is out of spec, you loosen the hold down clamp on the bottom of the distributor, and turn it slightly one direction or the other until your timing marks show up to where the spec label states.
When done tighten the distributor hold down bolt, and recheck your timing to make sure it didn't move. Turn off your engine, and reconnect everything as to how it was before you started. Make sure to remove the jumper wire you installed too.
Added by AMC EN member "canoe"
Did your buddy borrow your timing light and never return it? Here's a trick I learned from my brother. The timing can be set to surprising accuracy with a vacuum gauge. Hook the gauge to manifold vacuum and run the engine at curb idle. Rotate the distributor clockwise to retard the timing. Now slowly rotate it counter-clockwise to the point where you just reach the maximum vacuum reading. Back off (clockwise) until the vacuum drops by 1". Lock the distributor down. Timing can be set to within 1° using this method.