When your small engine-powered lawn mower, snowblower, or string trimmer won't start, it's often due to a faulty spark plug or ignition system. A simple spark check can help diagnose the issue. This guide walks you through the process, ensuring your engine is back up and running in no time.
Before we dive in, ensure your engine is cool and you have the necessary safety gear, including gloves and safety glasses. Also, gather your tools: a spark plug wrench, a feeler gauge (for adjusting the spark plug gap), and a spark plug tester or a screwdriver with an insulated handle.
Understanding the Spark Plug and Ignition System
The spark plug ignites the air-fuel mixture in your engine's cylinder. The ignition system, consisting of the spark plug, spark plug wire, and ignition coil, generates the electrical spark. If the spark plug is fouled or the ignition system is faulty, your engine won't start.
Performing a spark check helps identify if the spark plug or ignition system is at fault. Let's explore how to check the spark and troubleshoot common issues.
Checking the Spark Plug
Remove the spark plug using a spark plug wrench. Inspect the plug for signs of fouling, such as a dark, oily, or wet appearance. A fouled plug may need cleaning or replacement. Use a feeler gauge to adjust the spark plug gap if necessary (consult your engine's manual for the correct gap).
Reinstall the spark plug, ensuring it's securely tightened. Now, let's check the spark.
Checking the Spark
Attach the spark plug tester to the spark plug, ensuring the metal tip touches the spark plug's electrode. Ground the tester by touching its metal body to a metal part of the engine, like the engine block. Ask a helper to pull the starter cord or engage the electric start. You should see a strong, blue spark jumping the gap between the electrode and the tester's tip.
If there's no spark or a weak spark, the spark plug may be faulty, or there could be an issue with the ignition system. Let's troubleshoot further.
Inspecting the Ignition System
If the spark plug checks out, the issue might lie within the ignition system. Inspect the spark plug wire for any cracks, frays, or damage. Replace it if necessary. Next, examine the ignition coil for any signs of damage or leaks. If it's faulty, replace it.
If the ignition system components seem intact, the issue might be with the ignition switch or wiring. Inspect the wiring for any breaks, frays, or corrosion. Test the ignition switch using a multimeter to ensure it's functioning correctly.
Testing the Ignition Switch
Set your multimeter to the ohms setting. Disconnect the ignition switch's wire harness. Touch one multimeter probe to each terminal on the switch. The resistance should change when you turn the ignition key to the 'on' position. If there's no change in resistance, the switch is likely faulty and should be replaced.
If the ignition switch checks out, the issue might be with the wiring or connections. Inspect the wiring harness and connectors for any signs of damage or corrosion. Repair or replace as necessary.
With the spark check and ignition system troubleshooting complete, your small engine should now be ready to start. If you've replaced any components, ensure they're properly installed and adjusted according to the manufacturer's instructions. Always test your engine in a safe, open area, away from flammable materials.