Timing light guns are an invaluable way of doing a quick check of the ignition timing. Of course the bike must be in running order first (the timing must be set statically during an engine rebuild, for instance), but for precise running timing checks, the light gun is invaluable.
The early light guns were little more than a gun-shaped unit that flashed a light every time a spark fired on the cylinder or spark plug being fired.
Current models have LED displays showing RPM, angle of ignition, and RPM.
Running Engines
The biggest drawback of a timing light gun is the fact that the engine must be in a running condition first. In other words the timing light gun can be only used to check the statically set timing.
Setting the timing on many classic motorcycles is relatively easy but is nonetheless very important to the running condition of the engine. There are two main types of ignition on classic motorcycles: fully electronic or contact points. The main difference between these types is the triggering or switching system used to initiate a spark at the plug. The contact point set up uses a mechanical method for this switching whereas the fully electronic system is achieved with an electromagnetic trigger arrangement. Both types can be checked (after setting statically) with the timing light gun method.
Note: See Setting Ignition Points Gap
Assuming the ignition has been set statically, the timing light gun can be used to optimize the ignition settings by checking the dynamic spark position.
Attaching the Timing Light Gun
Most timing light guns follow the same attachment process, that being: with the engine switched off, a clamp is attached to the HT (high tension) lead, and a positive and negative lead is attached to the bike’s battery (an auxiliary battery can be used to supply electrical current to the gun, such as when working on flywheel magneto type ignitions). Before checking the ignition timing with the gun, it is good practice to clearly mark the timing marks on the flywheel. On dry running flywheels the mark’s visibility can be increased with the use of chalk, and on wet (running in oil) units, a paint mark will help.
The engine should be started and warmed to its operating temperature (no choke needed). The idle speed should be set and the timing light gun pointed at the timing window. The flashing light will freeze the timing marks.
Note, it is important to determine from the bike’s manufacturer what the RPM should be for the idle check and the fully advanced check.
Dynamic Adjustment
If the ignition system uses an adjustable plate (where the points are located, or where the magnetic pickup are) the mechanic can slowly rotate the plate until the correct ignition timing is found. The adjustable plate should have its locating screws tightened at this point and the ignition marks checked again. Assuming the timing did not move, the mechanic can now increase the RPM to check the ignition advance. Often it is necessary to set the timing by compromising between the idle setting and the advanced setting. Most mechanics will favor the advanced settings as this is where the engine will spend most of its running time.
Note:
Basic Ignition Timing Tech.
To complete a successful running condition, an internal combustion engine must have 1) compressed fuel in the correct ratio and 2) a system of ignition that fires the compressed fuel at precisely the right time—as in ignition timing.
Most manufacturers will specify the static and fully advanced ignition positions, and occasionally the dwell angle. However, the later requirement (found on some motorcycles with contact point ignitions) is much less important that the ignition point. Note: The dwell angle is the amount of time (or angle) that the points are closed and the ignition coil/s are being charged. While a greater dwell angle is better, increasing the dwell angle too far can lead to a retarded ignition condition.
The early light guns were little more than a gun-shaped unit that flashed a light every time a spark fired on the cylinder or spark plug being fired.
Current models have LED displays showing RPM, angle of ignition, and RPM.
Running Engines
The biggest drawback of a timing light gun is the fact that the engine must be in a running condition first. In other words the timing light gun can be only used to check the statically set timing.
Setting the timing on many classic motorcycles is relatively easy but is nonetheless very important to the running condition of the engine. There are two main types of ignition on classic motorcycles: fully electronic or contact points. The main difference between these types is the triggering or switching system used to initiate a spark at the plug. The contact point set up uses a mechanical method for this switching whereas the fully electronic system is achieved with an electromagnetic trigger arrangement. Both types can be checked (after setting statically) with the timing light gun method.
Note: See Setting Ignition Points Gap
Assuming the ignition has been set statically, the timing light gun can be used to optimize the ignition settings by checking the dynamic spark position.
Attaching the Timing Light Gun
Most timing light guns follow the same attachment process, that being: with the engine switched off, a clamp is attached to the HT (high tension) lead, and a positive and negative lead is attached to the bike’s battery (an auxiliary battery can be used to supply electrical current to the gun, such as when working on flywheel magneto type ignitions). Before checking the ignition timing with the gun, it is good practice to clearly mark the timing marks on the flywheel. On dry running flywheels the mark’s visibility can be increased with the use of chalk, and on wet (running in oil) units, a paint mark will help.
The engine should be started and warmed to its operating temperature (no choke needed). The idle speed should be set and the timing light gun pointed at the timing window. The flashing light will freeze the timing marks.
Note, it is important to determine from the bike’s manufacturer what the RPM should be for the idle check and the fully advanced check.
Dynamic Adjustment
If the ignition system uses an adjustable plate (where the points are located, or where the magnetic pickup are) the mechanic can slowly rotate the plate until the correct ignition timing is found. The adjustable plate should have its locating screws tightened at this point and the ignition marks checked again. Assuming the timing did not move, the mechanic can now increase the RPM to check the ignition advance. Often it is necessary to set the timing by compromising between the idle setting and the advanced setting. Most mechanics will favor the advanced settings as this is where the engine will spend most of its running time.
Note:
Basic Ignition Timing Tech.
To complete a successful running condition, an internal combustion engine must have 1) compressed fuel in the correct ratio and 2) a system of ignition that fires the compressed fuel at precisely the right time—as in ignition timing.
Most manufacturers will specify the static and fully advanced ignition positions, and occasionally the dwell angle. However, the later requirement (found on some motorcycles with contact point ignitions) is much less important that the ignition point. Note: The dwell angle is the amount of time (or angle) that the points are closed and the ignition coil/s are being charged. While a greater dwell angle is better, increasing the dwell angle too far can lead to a retarded ignition condition.