Disconnect the battery: First, disconnect the negative terminal of the battery to ensure that the power is off before proceeding with the diagnosis.
Locate the CDI unit: On the 2001 Yamaha Big Bear, the CDI unit is located under the front left fender, beneath the fuel tank.
Check for spark: Before testing the CDI, ensure that there is proper spark present. Disconnect the spark plug wire from the spark plug and hold it close to the cylinder head while someone cranks the engine over. If you see a good, strong spark, proceed to the next step.
CDI connection points: On the CDI unit, there are three connection points, usually referred to as "C-L","P," and "G." Check for continuity within the "P," "G," and ignition coil terminal, as well as resistance measurements based on factory service manual specifications in your case the "01 Yamaha Big Bear service manual." Any deviation may imply faulty ignition system components causing engine problems. Verify the values with the service manual, and if found out of specification, you might need replacement components like the CDI unit ignition coil etc…
