You have your numbers in hand. Your tools are within reach. Now, it's time to start. Or at least start the timing light, one of the most critical tools in your arsenal.
A timing light is simply a strobe light timed to flash on and off as the spark plug at cylinder No. 1 sparks on and off. This light is aimed at specific timing marks on the engine, and the two coordinate to time the ignition system to engine rotation as the car is running. In short, this is dynamic timing.
The timing light has three leads: one for battery positive, one for battery negative and one that clamps on to the cylinder No. 1 spark wire. Hook the leads up, and check to see if the light works.
Find the timing marks on the engine. Most are on the crankshaft pulley and block, but some systems have them in other locations. There will be two marks. Make sure these are visible by either cleaning them, or marking them with bright paint or chalk.
Now, refer to your timing specifications. Let's assume your car is a 1969 Ford Mustang with an automatic transmission and a 429 engine. The factory manual stated ideal timing was 6 degrees BTDC measured with engine idling at 600 RPM in gear.
With the vacuum lines to distributor disconnected, the marks chalked in and the timing light hooked in correctly, it's now time to start the engine.
Aim the timing light at the mark and press the trigger. The marks should look like they're standing still. If the two lines are lined up, your engine is timed correctly and there's no further work. If they're not, it's time to adjust the timing. This is accomplished by adjusting the distributor.
Loosen the distributor hold-down clamp enough to allow the distributor to rotate on its central shaft. Rotate the distributor slightly, only a few degrees one way or the other. Check your marks with the light. If they're farther apart, rotate the distributor a few degrees in the opposite direction from the way you first turned it. If the marks were closer together, keep rotating in the original direction.
Once the timing is correct, tighten the hold-down, and then recheck the marks. Sometimes, tightening the distributor can change the timing.
While the timing light is connected, reconnect your vacuum hose to the distributor, and check to see that the vacuum advance is working correctly. If it's working, you can see the marks shift apart as the RPM is increased or move closer together as it decreases.
Once you understand timing's basic techniques, the process is fairly simple and straightforward. In fact, properly timing and engine can extend its useful life, make it more efficient and better-performing.