Testing Igniters for Electrical Leakage

A simple way to test igniters for electrical leakage without disassembly

| November/December 1978

  • Igniter tester

  • Igniter tester

Not long ago many helpful answers were printed for the benefit of someone who asked how one could tell if an igniter was working properly. However, I don't believe any of them mentioned the possibility of electrical leakage or shorting in an igniter, or how to test an igniter for electrical leakage. The igniter is, after all, a primitive spark plug, and like its high tension cousin, can spark quite beautifully outside the engine, but still neither one may function under compression.

When an igniter seems to give a "good" spark outside the engine, magneto/battery-coils have been checked and seem to be working efficiently, yet when the igniter is bolted to the engine and the latter is either very difficult to start or won't start at all, there is probably low-tension electrical leakage through the insulated electrode.

There is a simple way to check electrical leakage without disassembly of the insulated electrode. First, buy or borrow a 110 V. neon circuit tester. Most hardware stores have them. They cost very little and are valuable for testing house circuits. Then attach two alligator clips to the bare ends of an old extension cord that still has the male plug attached, and set up a circuit as follows:

Plug the extension cord into a socket, being sure that the alligator clips don't short on the igniter frame. Igniter points must be open. Now touch the free lead of the neon light to the inner part of the insulated electrode. It should light up brightly. Next touch the same lead to the igniter base or "hammer." Note, and this is important: If the igniter is in good condition, the bulb should not light at all. Any degree of lighting of the bulb indicates electrical leakage through the insulation. The leakage may be little enough to allow starting the engine, but again it may not. To be safe, disassemble the insulated electrode, remove all the insulation, especially that portion that is subject to heat and carbon formation within the cylinder, and clean or preferably replace it with new. Then reassemble and test again with the neon light. If no leakage exists, the igniter will be O.K. electrically.

Contact Doc Shuster at 3535 Glen Oak Drive, Eugene, Oregon 97405. 


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