To replace it, shut off and cool the engine, disconnect the spark plug boot, remove the old plug, install a new one with the correct gap and torque, then test the mower.
What you’ll need
Gather the right plug, tools, and safety gear before you begin to minimize delays and avoid damage.
- Correct spark plug for your Honda engine (check the owner's manual or the old plug for the recommended heat range and thread size; Honda engines commonly use NGK or Denso equivalents, but always verify for your model).
- Spark plug socket and ratchet (typically 13/16-inch or 5/8-inch, depending on the plug).
- Gap tool (feeler gauge) to set the proper electrode gap, typically around 0.030 inches (0.76 mm) unless your manual specifies a different value.
- Clean cloths or a small brush to clean debris from around the plug.
- Torque wrench or a standard wrench to achieve the correct snug-tightening torque (often roughly 12–20 N·m / 9–15 ft-lb; refer to your manual).
- Safety gear: gloves and eye protection.
- Dielectric grease for the spark plug boot (optional but helps seal and ease removal).
With the right plug and tools on hand, you’re ready to proceed to the replacement steps.
Choosing the right spark plug
Identify your engine model
The exact plug type and gap depend on your mower’s engine model and serial number. Check the mower’s label or owner's manual, or pull the old plug and match it at an auto parts store. Using the correct heat range and thread size helps reliable starting and prevents fouling.
Step-by-step replacement
Follow these steps in order to ensure proper installation and safe operation.
- Ensure the mower is off, parked on a level surface, and the engine is completely cool.
- Disconnect the spark plug boot by firmly pulling it straight off the metal plug terminal to avoid damaging the wire.
- Clean the area around the spark plug to prevent debris from entering the combustion chamber when you remove the plug.
- Using a spark plug socket, ratchet, and extension if needed, carefully loosen and remove the old plug by turning it counterclockwise.
- Inspect the old plug’s condition. A white or pale center electrode indicates lean misfire; heavy fouling or oil on the threads may signal other issues.
- Check the gap on the new plug. Most small Honda engines use a gap around 0.030 inches (0.76 mm); adjust with a gap tool if necessary.
- Thread the new plug in by hand to avoid cross-threading, then tighten to the recommended torque level (consult your manual). If you don’t have a torque wrench, snug the plug and give it another quarter to half turn beyond snug.
- Reconnect the spark plug boot, optionally applying a small amount of dielectric grease to the inside of the boot for a better seal and easier future removal.
- Start the mower and listen for smooth operation. If it sputters or won’t start, recheck the plug and air filter; ignition issues may require professional service.
Once the replacement is complete and tested, you’re ready to resume normal mowing with improved reliability.
Care after replacement
Keep the area around the spark plug clean and dry, recheck the boot’s connection after a few minutes of operation, and consider replacing the air filter if it’s dirty, as a clogged air filter can affect combustion and plug fouling.
Summary
Replacing a Honda lawn mower spark plug is a quick, practical maintenance task. Identify the correct plug for your engine, gather the tools, set the gap as specified, and tighten to the recommended torque. Always work with the engine cool, disconnect the spark plug boot before touching the plug, and test the mower after installation. Regular plug maintenance helps ensure reliable starts, efficient combustion, and better mowing performance.