How do you test a magneto?

Answer

You will need end wrenches and volt ohmmeter. Detach the flywheel shroud using an end wrench to find the magneto which is connected directly to the spark plugs. Remove the rubber coated wire from the spark plug and remove the small bolt securing the groundside wire to the engine case. Make sure that the ground wire does not touch the engine case as this will give a false reading. Move the ohmmeter to ohms touch the red probe to the ground wire before touching the black probe to the spark plug clip which should give you a direct short or continuity. Detach the black probe from the clip and touch it to the engine case which should give you infinite ohms or wide open reading. Reattach the ground wire to the engine case and switch the volt ohmmeter back to volts before selecting the high voltage reading. Touch the spark plug clip with the red probe and the black end of the probe to the engine case before rotating the flywheel past the magneto a few times. Reattach the flywheel cover; insert the spark plug back into the rubber hood laying the plug against the metal frame of the engine.
1 Additional Answer
Remove the flywheel shroud with the end wrench or sockets. The magneto is the only part with exposed copper windings. It will have a large, rubber-coated wire coming from it and is directly connected to the spark plug. Another smaller wire will be connected directly to the metal case of the engine body. Pull the rubber-coated wire from the spark plug. Inside the rubber hood, there is a round clip that fits over the end of the spark plug. This is the high-voltage side of the magneto. Remove the small bolt that is used to secure the groundside wire to the engine case. Ensure the ground wire does not touch the engine case, or a false reading will occur. Switch the ohmmeter to ohms, and then touch the red probe to the ground wire and the black probe to the spark plug clip. The meter should then register a direct short or continuity. Reconnect the ground wire to the engine case. Switch the volt ohmmeter back to volts, and then select the high-voltage reading. Replace the flywheel cover, and then pull the spark plug from the cylinder head of the engine. Insert the spark plug back into the rubber hood, and lay the plug against the metal frame of the engine. Pull the start cord, and observe the end of the spark plug. As the engine turns on, the spark plug should emit a bright white spark. If no spark is generated, then the plug will have to be replaced.
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