How to Test a Magneto With a Multimeter

Are you facing troubles with your Magneto? Looking for ways to test if it’s working correctly?

How to test a magneto with a multimeter is a crucial step in diagnosing ignition system problems in small engines, such as those found in lawnmowers, chainsaws, or motorcycles. A magneto is responsible for generating the electrical spark that ignites the air-fuel mixture in the engine’s cylinder, and any malfunction can lead to difficulties in starting or maintaining engine performance. Using a multimeter, which measures electrical properties such as voltage, resistance, and continuity, can help identify potential issues with the magneto, such as broken wires or faulty connections.

In this guide, we will walk you through testing a magneto with a multimeter, ensuring you can accurately assess its functionality and efficiently address any underlying issues.

What Will You Need?

To perform the tests outlined in this guide, you will need a few essential tools and materials:

• A multimeter with probes
• Safety glasses
• A set of basic hand tools (screwdriver, pliers)
• A new spark plug (optional)
• Your magneto manual or engine manual (for reference)

It’s always important to ensure your safety while working with small engines. Wear safety glasses to protect your eyes from any debris that may fly out during the testing process.

9 Easy Steps on How to Test a Magneto With a Multimeter

Step 1: Preparing Your Multimeter

Before starting, ensure your multimeter is in good working condition and appropriately set. Begin by setting your multimeter to the resistance (ohms) setting, which is vital for checking the continuity and resistance level of the magneto. Consult the multimeter’s manual if you need clarification on adjusting the settings. Next, inspect the probes; they should be clean and undamaged for accurate readings.

Attach the black probe to the standard (COM) port and the red probe to the VΩmA port on the multimeter. It’s a good practice to test the multimeter by connecting the two probes together to confirm a zero- ohms reading, indicating that the meter is correctly calibrated for accurate measurements. This preparation will ensure that you’re ready to proceed efficiently with the magneto testing process.

Step 2: Access the Magneto

To access the magneto, you will need to remove any covers or parts that obstruct it. This typically involves taking off the engine cover or flywheel housing, which can usually be done using a screwdriver. Be sure to consult your magneto or engine manual for specific instructions on dismantling these components, as the procedure may vary depending on the make and model of your engine. Once you have access to the magneto, visually inspect it for any obvious signs of damage, such as worn-out wires or loose connections. Identifying visible issues early can save time during the diagnostic process.

Step 3: Disconnect the Magneto Wires

To accurately test the magneto, it’s essential to disconnect it from the engine circuit. Begin by carefully identifying the wires that connect the magneto to the ignition system. These are typically accessible once the covers are removed. Use pliers or a suitable tool to gently disconnect the wires, ensuring that they do not damage or fray during the process. Note their attachment points for reassembly later, and keep track of any screws or fasteners removed. This step is crucial for isolating the magneto, allowing you to conduct tests without interference from other engine components. Ensure the engine is off and all power sources are disconnected to maintain safety while working.

Step 4: Test for Continuity in the Magneto Coils

Next, the multimeter is used to test the magneto coils for continuity. With the multimeter set to the resistance (ohms) setting, place one probe on one of the magneto’s wire terminals and the other probe on the opposite terminal. A good magneto coil should indicate continuity, which means the current can flow uninterrupted through the coil. If the multimeter shows a very high resistance or “OL” (over limit), the coil is likely faulty, and the magneto may need to be replaced. Record your readings as you test each coil, as this information will be helpful in identifying which parts are functioning correctly and which may require further attention.

Step 5: Measure the Resistance of the Primary Winding

To test the primary winding of the magneto, keep the multimeter set to measure resistance (ohms). Place one probe on the primary wire terminal and the other probe on the body of the magneto. This will measure the resistance of the primary coil winding. Refer to your magneto or engine manual for the expected resistance range, as it can vary between models and manufacturers. If the resistance reading falls outside this range, it indicates an issue with the primary winding, and the magneto may need repair or replacement.

Step 6: Measure the Resistance of the Secondary Winding

With your multimeter still set to the resistance (ohms) setting, proceed to measure the secondary winding. Place one probe on the high-tension (HT) lead, typically where the spark plug wire connects, and position the other probe on the magneto ground or the metal casing. The resistance reading for the secondary winding is generally higher than that of the primary winding.

Again, compare your findings with the specifications outlined in your magneto or engine manual to determine if they fall within the acceptable range. If the resistance is outside this range, it suggests a problem with the secondary coil, potentially affecting the magneto’s performance. Accurately documenting these readings is essential for troubleshooting and can provide a valuable reference if professional repairs are needed.

Step 7: Inspect the Spark Plug Connection

Once you have completed testing the magneto coils and windings, the next step is to inspect the spark plug connection. This connection is critical for transmitting electrical impulses from the magneto to the spark plug, igniting the air-fuel mixture in the engine. Examine the spark plug lead for any cracks, corrosion, or damage that might impede the electrical flow. Use the multimeter to measure the resistance from the magneto’s end of the spark plug lead to the spark plug terminal. The resistance should align with the specifications provided in your magneto or engine manual. If the readings are inconsistent or the connection appears compromised, replacing the spark plug lead may be necessary to ensure proper engine function.

Step 8: Reassemble the Engine Components

After completing all necessary tests and inspections, it’s time to reassemble the engine components. Begin by carefully reattaching any wires you previously disconnected, ensuring that each connection is secure and corresponds to its original attachment point. Reinstall the engine cover or flywheel housing using the screws or fasteners you retained, referencing your magneto or engine manual to confirm the correct procedure and order. Double-check that all components are fitted snugly, with no loose parts that could affect the engine’s operation. Once everything is back in place, you can proceed to reconnect the power source and start the engine to verify that the magneto and ignition system are functioning correctly.

Step 9: Perform a Final Operational Test

Once the engine components have been reassembled and all connections verified, conducting a final operational test is crucial. Start the engine to ensure that it runs smoothly, and the ignition system is functioning as expected. Listen for any unusual sounds, such as knocking or misfiring, which could indicate lingering issues with the magneto or other components. Observe the engine’s performance under various conditions, checking for steady operation at both idle and higher RPMs. If any problems persist, revisit the previous steps to re-inspect your work or consult a professional technician for further diagnosis.

By following these steps and conducting regular maintenance and inspections, you can ensure the proper functioning of your magneto and ignition system.

5 Things You Should Avoid

1. Avoid Using a Digital Multimeter on Magnetos with High Voltage: Digital multimeters are often not designed to handle the high voltage some magnetos generate. Using them can damage the multimeter or provide inaccurate readings.
2. Don’t Test with the Engine On. Always ensure the engine is off before testing a magneto. This precaution prevents accidental shocks and ensures the safety of both the user and the equipment.
3. Avoid Overlooking Safety Gear: Please wear appropriate safety gear, such as gloves and protective eyewear, to avoid injuries. Always prioritize safety by wearing the right gear before handling electrical components.
4. Do Not Forget to Check the Multimeter Settings: Before testing, ensure that the multimeter is set to the correct measurement setting. Incorrect settings can lead to misleading results or damage to the device.
5. Avoid Skipping a Visual Inspection: Before using a multimeter, inspect the magneto for obvious signs of wear or damage. Addressing any issues beforehand can ensure accurate test results and potential harm.

Conclusion

How to test a magneto with a multimeter requires careful attention to safety and precision.

You can effectively test without risking injury or equipment damage by adhering to the outlined precautions, such as avoiding high voltage settings on your multimeter and ensuring the engine is off. Always wear safety gear and double-check your multimeter settings to maintain accurate readings. Furthermore, conducting a thorough visual inspection of the magneto helps identify potential issues before testing, ensuring the process is safe and efficient.

By following these guidelines, you can ensure that your magneto testing endeavors are prosperous and secure.