Testing motorcycle CDI units
⚠️ Safety Warning: Electrical troubleshooting often involves working near the battery and fuel system. Ensure there are no fuel leaks before testing for sparks, and always disconnect the battery before removing electrical components like the CDI to avoid short circuits.
Testing the CDI Unit on Yamaha YZF-R125
If your bike is turning over but failing to start, or if you are experiencing intermittent cutting out, the CDI (Capacitor Discharge Ignition) unit may be the culprit. This component is the "brain" of the ignition system, controlling the timing of the spark.
Signs of a Faulty CDI
No Spark: The most common symptom where the plug simply won't fire despite a good battery and coil.
Misfiring: Erratic engine behavior or backfiring caused by incorrect ignition timing.
Intermittent Starting: The bike starts fine one day but refuses the next, often affected by temperature or vibration.
Troubleshooting Steps
Check Connections: Ensure the multi-plug connector to the CDI is clean, dry, and free from corrosion.
Visual Inspection: Look for any signs of "bulging" or burnt casing on the unit itself.
Voltage Test: Use a multimeter to ensure the CDI is receiving the correct input voltage from the stator/battery.
Component Bypass: Often, the best way to test is to temporarily swap with a "known good" unit to see if the fault clears.
Shop Replacement CDI Units
Replacement CDI/ECUs:
Shop Yamaha YZF-R125 CDI Units on eBay UK Electrical Spares:
General YZF-R125 Electrical Parts on eBay UK
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