Adjustable Timing Light - Light Up Performance

Distributor Recurve
Once you've determined the required amount of total spark lead for peak performance, you'll likely find that the distributor's centrifugal advance curve needs adjusting. The ideal method for that includes a professional-grade bench tester, but many hobbyists don't have such equipment readily available, nor is it always convenient to remove the distributor from the engine. An adjustable timing light and auxiliary tachometer can accomplish the same task while the distributor remains in the engine.After recording base timing, smoothly increase engine speed until the variable timing mark just begins to move and record that rpm point. Continue increasing engine speed until the variable timing mark quits moving, and record that timing and rpm point. You can then remove the cap and rotor (install a new timing limiter bushing) and test various advance springs and components until you find the combination that best suits your engine's spark lead requirements. Use caution when revving the engine, however, as high engine speed without a load could cause significant internal damage.

Idle Speed Made Simple
Not all adjustable timing lights are capable of registering engine speed, but Actron's Digital unit does, further increasing its usefulness to hobbyists. Simplifying any instance where an auxiliary tachometer is required, the integral unit in Actron's offering allows for easy engine speed monitoring when recurving a distributor. The operator can see either reading with just the push of a button. We also found it useful when setting engine idle speed.

Vacuum Advance Variety
A sufficient amount of vacuum advance can significantly improve throttle response in light load conditions, but too much can lead to audible detonation. While part-throttle detonation won't likely cause catastrophic engine failure (as long as it subsides as engine load increases), the sound will surely make any driver uneasy. An adjustable timing light can be used to determine just how much vacuum advance your Pontiac can tolerate.After setting base timing and properly adjusting the distributor's centrifugal advance curve, disconnect the vacuum advance unit and adjust the timing light until the variable and stationary TDC marks are aligned, and record the amount on the dial or digital display (this should be the same amount as base timing). Connect the vacuum advance canister to a manifold vacuum source or a handheld vacuum pump. Readjust the timing light so the variable and stationary marks are again aligned, and record that number. The difference between the two is amount of vacuum advance available. Installing another stock-type vacuum advance unit providing a lesser amount or an adjustable aftermarket piece should clear up any detonation with no ill performance effects.

Seeing Sparks Scatter
A timing light will only illuminate when its inductive clamp receives a strong electric impulse passing through a plug wire, which makes it a useful tool when attempting to locate a dead cylinder. However, an adjustable unit can make it much easier to locate a random misfire. By simply moving the inductive clamp from one wire to another and adjusting the strobe until a variable timing mark is visible, you can determine if the variable mark remains steady or is erratic or weak.