The CDI (Capacitor Discharge Ignition) unit decides when your bike sparks. It is a model-specific part, and even a small mismatch in pin count or ignition curve causes a no-start or a misfire. This guide explains how to buy the right CDI.
1. Match the exact model and pin count
CDI units differ by connector pin count (for example 4+2 or 8 pins) and by the ignition advance curve programmed for each engine. A CDI for one model will not run another correctly even if the plug fits. Use the exact model name and the stated pin count.
2. DC vs AC CDI
Some bikes use a DC CDI (powered from the battery) and others an AC CDI (powered from the stator source coil). They are not interchangeable. If your bike has a battery-fed CDI and you fit an AC unit (or vice versa), it will not spark reliably.
3. Symptoms of a failing CDI
A bad CDI commonly causes a total loss of spark, random misfiring, backfiring, a hard rev limit, or cutting out when hot. Because the ignition coil and pickup can cause the same symptoms, test those first.
4. Common causes of CDI failure
Voltage spikes, a faulty regulator rectifier, water ingress, and poor grounds shorten CDI life. If a replacement fails quickly, check the charging system and earths rather than blaming the part.
5. Fitting tips
Disconnect the battery, note the connector orientation, and mount the CDI where it is protected from heat and water. Confirm the earth connection is clean and tight.
Bottom line
Match the model (and its ignition curve), the pin count, and the DC/AC type. Get those right and the CDI is a plug-and-play fix.
Bike Model Fitment
| Bike Model | Year | Fits |
|---|---|---|
| Hero (Super Splendor, CD Dawn) | 2000-present | Yes |
| Bajaj (Discover 150, Pulsar DTSI) | 2000-present | Yes |
| Honda (Activa 110, CB Trigger) | 2000-present | Yes |
| Yamaha (R15 V3, FZ-S) | 2000-present | Yes |
| LML (CRD 100) | 2000-present | Yes |
Quick Mechanic Diagnostic Checklist
- Count the CDI connector pins
- Confirm DC or AC CDI type
- Match the exact model and ignition curve
- Test the ignition coil and pickup before replacing
- Inspect the wiring and earths
- Disconnect the battery before removal
- Keep the old unit as a reference
Frequently Asked Questions
What does a bike CDI unit do?
It stores and releases electrical energy to fire the ignition coil at exactly the right moment, setting your bike ignition timing. A wrong CDI changes timing and can stop the engine running correctly.
How do I know which CDI fits my bike?
Match the exact model and its pin count, and confirm whether your bike uses a DC or AC CDI. The product listing states the models and pin layout covered.
What are the signs of a bad CDI?
No spark, misfiring, backfiring, a low rev limit, or cutting out when hot. Test the ignition coil and pickup first, because they cause similar symptoms.
Are these CDI units genuine OEM?
They are OEM-spec replacements programmed to the original ignition curve, mounting, and connector. The listing names the exact models covered.
Why did my new CDI fail quickly?
Voltage spikes, a faulty regulator rectifier, water ingress, or a poor earth can damage a CDI. Check the charging system and grounds before fitting another.