Commonly Located: The capacitor discharged ignition is commonly referred to as a CDI box. The CDI box varies widely in its location. Each make and model will usually have the CDI box located in a different place. Normally, the CDI box is attached to the frame with twenty plus wires coming from the wiring harness and leading into the box.
Physical Description: The CDI box is normally square or rectangular. Factory boxes are almost always black plastic but aftermarket models can vary in color (red is pretty common). There is usually one to three plugins on one end of the box. This is where the CDI box connects to the wiring harness.
Occasionally, there may be additional wires coming from the box. The plugins can vary in appearance and size depending on the make and model of the ATV. CDI boxes are sometimes described by the number of pins in the plug. (This is especially common with both youth and Chinese ATVs.) The CDI box shown below is a 6-pin box.
Functions: The CDI box receives a pulse signal from the stator. It then calculates when the engine needs to fire the spark plug. At the appropriate time, the box sends a pulse to the ignition coil, when then fires the spark plug. (For more information on this process, see Anatomy of an ATV - Ignition Coil. Total, the CDI box controls the reverse limiter, the timing, the spark, the rev limiter, and all factory safety kill switches. Depending on the make and model of the ATV, the CDI box can also control a number of other things. For more information on your specific model, see the wiring diagram in the service manual.
Maintenance Costs: The price of a CDI box can vary between make and model but is one of the more expensive parts to replace. A couple hundred to replace a CDI box is pretty common. Fortunately, the CDI box is NOT a common wear item, despite often being blamed for starting issues. The only way to definitively determine the cause of starting issues is to properly troubleshoot all of the electrical components. It is NOT recommended to purchase a new CDI box without first verifying that all of the other components are working. Because there is no way to test a CDI box, it is never recommended to buy one used.