What Is a Pick-up Coil?

A pick-up coil is a simple device used to tell the CDI box when to fire the spark plug. On a flywheel, there are marks indicating where Top-Dead-Center of each piston is. Those marks are usually small bumps on the outer rim of the flywheel. The pick-up coil is mounted very close to those bumps and generates a small pulse every time one of them passes underneath it. The pulse is generated in the coil by the magnet in its center and is sent directly to the CDI box. From there, the CDI will determine when to fire the spark plug.