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Hook your timing gun up to the power and ground terminals on your car's battery, and hook the sensor that accompanies the timing gun to your number one cylinder spark plug wire. Follow the instructions particular to the timing light you're using to hook it up properly. The "gun" works by illuminating the timing marks in a strobe fashion as it spins, allowing you to see the point at which the spark plug is firing on the timing index. When the spark plug fires, the sensor sends a signal to the light, which strobes in the gun, illuminating the numbers at the proper moment. To check your timing number and see how it is firing, have someone rev the engine while you illuminate the timing numbers with your light. You obviously want to make sure the car is in neutral, and keep your hands a safe distance from the engine as it revs. Though the wheel is turning, the light should seem to "freeze" it at a particular number. This is the timing number. Note the number of degrees to the right or left of zero. As the RPMs increase, the point at which the spark plug is firing should also increase somewhat. This is normal, because ignition works on a curve, allowing for the speed increase and adjusting the timing accordingly. To check for total timing, you want to be sure to rev the engine to at least 3500 RPMs. This will allow you to make sure the curve of the ignition timing is being set, as well as the initial timing. If your car features vacuum timing advance in addition to mechanical timing, and you'll need to loosen the distributor adjustment bolt before you start the engine. Next, remove the vacuum advance hose from the carburetor and plug it with a rag to check your timing. Vacuum timing works by making minor adjustments at at low RPM by rotating slightly to adjust for the timing. Now that you've found your ignition timing number, how do you know if you need to adjust it? All models of cars will have differing timing values, depending on the year it was manufactured and the variety of transmission used. To learn whether or not you need to adjust your timing, find the optimum timing number for your make and model and adjust if necessary. If you don't know your timing number, talk to a licensed mechanic or employee at your local auto parts store to consult their manuals and find the proper timing number.
Hook up your timing light or timing gun. Have a helper rev the engine. Shine the light directly onto the harmonic balancer and find the number. Account for vacuum timing, if necessary. Adjust the timing, if necessary.