Motorcycle ignition coils play an important part in making the bike run, if they don’t work the bike won’t be able to produce a spark at the spark plug so the motorbike won’t run.
What does the motorcycle coil do?
Basically, the coils job is to produce a spark at the spark plug which ignites the fuel/air mix in the engine cylinder.
However, this isn’t as simple as it sounds as a bikes electrical system usually runs on 6 or 12 volts (slightly more with the engine running) and the spark at the plug is roughly around 15 to 20,000 volts (yes, 15 to 20 thousand volts!).
So the coil has to convert 12 volts into 15 to 20,000 volts to ignite the fuel.
Note – Be careful if you testing the spark with the plug out of the engine not to have your hands or fingers near the plug or touching the engine as you are likely to get one hell of a shock!
The 3 parts of the motorcycle coil, the ignition coil, HT (high tension) lead and spark plug cap
Output end of the ignition coil
Input end of the ignition coil
Different parts of the outside of a motorcycle coil
The output from the coil connects the the HT lead (which connects to the spark plug), the input terminals connect to the CDI (the CDI sends a ‘pulse’ through these terminals telling the spark plug when to spark). The larger/central connectors on each end are the earth connections for the coil.
Length way internal components of the coil showing the primary and secondary coils and the iron core.
Cross section of a motorbike coil showing the internal components.
The coil works by generating a magnetic field using coils (often made from copper) around an iron core. More detailed information about magnetic field and coils can be found here
Like all motorcycle parts, coils can start to fail with age, symptoms of a coil starting to fail can be:
- Bike being very difficult to start or not starting at all.
- Rough running engine.
- Engine misfiring.
- Strong petrol smell from exhaust (cause by the spark not burning all the fuel).
- Increase in the amount of fuel used.
- Engine management light coming on (on later bikes that actually have this light!).
- No spark at the spark plug
Note – There are other problems and parts on a motorcycle that can cause the above problems and sometimes these symptoms can be caused because the HT lead or plug cap has worked loose.
Combined plug coils and caps from a Yamaha YZF-R1 engine.
Alot of later motorcycles use combined ignition coils and spark plug caps (also called ‘coil on plug’ systems) which does away with the need for HT leads and a separate coil.
Thanks to:
Good site with lots of good info about coils: dualwheeljourney.com
Information about spark plugs: https://bikerestart.com
Disclaimers:
The information provided on this page is ‘to the best of our knowledge’ and should not be taken as 100% accurate!!
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