The Pulser Coil, (often called Pickup Coil, or Timing Coil) is responsible for providing the timing signal to the ignition control box on modern motorcycles with solid-state ignition systems. The majority of motorcycles from the late 1970's and up use this system for reliable, accurate, and low maintenance ignition control. On previous models, points-controlled systems were used, and while cheap and simple, they required routine maintenance and component replacement to ensure reliability.
On most motorcycles up until the late 1970's, timing and spark control was done with a set of cam-driven points, which were mechanically advanced or retarded to control timing. The points would make contact, allowing current to build up. When the points were opened, and contact broken, the current was discharged through a coil to step up the output to high voltage in order to produce an ideal spark across the spark plug. This system was very simple, and similar to the system used on automobiles. The common replacement parts are the points, which wear down from constant friction as they open and close, and the condenser, which is a small capacitor to prevent arcing and premature wear & failure of the points. Timing is handled via a mechanical advance system. The timing of the points openening is advanced before Top-Dead-Center of the engine at higher RPM's, usually by means of a spinning weight.
Modern ignition systems use a solid state (semiconductor) controller to handle the ignition spark timing. The control box, often called a CDI box, or black box, handles multiple functions. The internal electronics are either powered from the battery (DC ignition systems, most street motorcycles), or in AC directly from the stator (most dirt/offroad motorcycles). Current from either the stator or the battery is used to charge up an internal capacitor. This capacitor is then discharged through the ignition coil via the spark plug to generate the very high voltage necessary for a good spark. The CDI box has digitally stored timing maps, to handle advance of the ignition depending on RPM, and sometimes other variables, such as a throttle position sensor (often called TPS, a sensor which varies it's resistance based on the opening of the throttle). The CDI box is fed timing data from the Pulser Coil, which produces a short duration, low current, high voltage pulse in relation to the Top Dead Center (TDC) piston location in the engine. This is explained more in depth below.
The pulser coil is a very simple component. It is generally housed in a small plastic container, and internally potted with epoxy or some other oil resistant material. The pulser coil itself is made up of a small magnet (the exposed metal you can see on the front of the housing), which is wound with a coil of very fine wire. The pulser coil may have one or two wires exiting the case to connect to the ignition box. On one wire systems, on side of the internal coil is grounded to chassis ground through the mounting hardware. On two wire systems, a wire from each side of the coil exits the case to connect to the ignition box.
The pulser coil generates it's timing pulse with help from the flywheel (Refer to the illustration above). The outside diameter of the flywheel has at least one timing mark, which consists of a raised ridge, spanning some percentage of the outer edge of the flywheel. This ridge is pronounced, and has sharp leading and trailing edges. The Pulser Coil is mounted to the engine sidecase in very close proximity (some thousands of an inch) to the flywheel, spaced to be extremely close to the timing ridge(s). The timing ridge is referenced to the Top-Dead-Center (TDC) piston location inside the engine. As the timing ridge on the flywheel spins past the pulser coil, the timing signal is generated. The leading and trailing edges of the raised metal ridge produce a low current, high voltage pulse, either positive then negative polarity, or negative then positive, depending on the direction of the coil winding inside the pulser coil. The ignition box then uses this signal to reference the piston location, and given it's inputs (RPM and TPS) it will determine the correct time to fire the spark plug, by discharging the internal capacitor out to the ignition coil, and finally the spark plug.
The Pulser Coil, as a unit, is not usually serviceable. It is a sealed component, and should be replaced if determined to be a problem. Pulser Coil problems sometimes manifest themselves in hard starting situations, but usually failures result in no spark at all. When the pulser coil fails it will usually produce no output pulse, or a very weak one. This is hard to verify, without special tools such as an oscilloscope to view the pulse. The usual failure is similar to a stator failure mode, the wire coil inside fail with the insulation breaks down and a short occurring, or the wire breaks inside causing an open circuit. The wiring external to the pulser coil assembly can be damaged as well, causing a connection issue. The only real troubleshooting method is to check the resistance of the Pulser Coil wires, to ensure they match known specifications, making it likely the coil inside is intact.
1: Lookup Pulser Coil technical specifications for coil resistance. These are available from the bike's service or owners manual, or our website's product page for our coils.
2: Obtain a Digital MultiMeter (DMM). Set to the hundreds resistance range if the meter is not auto-ranging.
3: Attach each meter lead to one wire from the pulser coil. If there is only one wire exiting the pulser coil, attach one meter lead the wire, and one to the metal mounting foot of the pulser coil housing.
4: Verify resistance reading matches the known specification. For most Pulser Coils this in the range of 180ohms-300ohms, but please compare to exact specifications for your part.
5: If either an short is detected (no resistance), or an open (OL - overload, on most meters), the coil is definitely bad.
6: There are no serviceable parts in a pulser coil, short of repairing a damaged section of the wiring harness. Please replace with a new coil.