Final answer:
A defective primary capacitor in a magneto is indicated by burned and pitted contacts, often resulting from the breakdown of its insulating material which causes arcing and damage to the contacts.
Step-by-step explanation:
A defective primary capacitor in a magneto is indicated by burned and pitted contacts. Capacitors consist of metal foils separated by an insulating material such as mica, ceramic, paper, or Teflon™, all of which are encased in a protective coating. When a capacitor fails, it often results from a breakdown of the insulating material, causing the two metal plates (or foils) inside the capacitor to come into contact. This unintended contact can produce electrical arcing which leads to the contacts becoming burned and pitted. In a magneto, the capacitor works to suppress the spark and protect the contact surfaces; thus, a malfunctioning capacitor cannot perform its role, and the evidence of this failure often appears on the contacts of the ignition points. Moreover, similarly to how small scratches in a protective paint coating on iron can lead to corrosion and eventually rust, holes or defects in the protective coating of a capacitor allow for unwanted chemical reactions that compromise the capacitor's integrity. Such defects in a magneto's capacitor are critical since they can result in engine misfires or poor engine performance due to improper timing of the spark. Therefore, regular inspection of the capacitor's condition is essential for maintaining a well-functioning magneto system.