How do I check, clean and change small engine spark plugs?
The electrodes on a spark plug must be clean and sharp to produce the powerful spark required for ignition. The more worn or dirty spark plugs are, the greater the tug on the rewind and more effort is required to produce an adequate spark.
If you haven't turned on your engine recently, your mower won't start and/or you have to tug repeatedly on the rewind to start the engine, a damaged spark plug may be the culprit. These problems may also cause excessive fuel consumption, deposits on the cylinder head and oil dilution.
Luckily, spark plugs are one of the easiest and most inexpensive engine components to replace.
For standard lawn mower and small engine maintenance, you should check and/or replace spark plugs:
- Annually and in accordance with the Operator's Manual
- If your lawn mower or outdoor power equipment won’t start
To check if your spark plug has gone bad you'll need to inspect your part for common signs suggestive that it might be fouled or damaged. Check out the steps below which outline how to determine why your spark plug is no longer working correctly.
- Step 1- Disconnect the spark plug lead. Clean the area around the spark plug to avoid getting debris in the combustion chamber when you remove the plug.
- Step 2- Remove the spark plug using a spark plug socket.
- Step 3- Inspect the spark plug for very stubborn deposits, or for cracked porcelain or electrodes that have been burned away. If any of these conditions exists, replace the spark plug.
- Step 4- Check the spark plug gap and adjust as necessary.
- Step 5- If it seems in working order, replace the plug, taking care not to over-tighten (15 ft. lbs. MAXIMUM) and re-attach the spark plug lead.
Review the FAQ on troubleshooting ignition system problems to learn how a spark tester can identify problems with the ignition coil, switch, flywheel or other small engine parts.
To safely clean a spark plug, you should use a wire brush or spray-on plug cleaner specifically designed for this ignition part.
Note: NEVER clean a spark plug with a shot blaster or abrasives.
If your spark plug doesn’t pass the tests above, then it has gone bad and you’ll need to replace it. This is one of the easiest steps in lawn mower or small engine maintenance.
For pre-season tune-ups and end-of-season storage, consider a Briggs & Stratton® small engine tune-up kit that includes everything you need, including parts (spark plug(s), oil filter, air filter) and fluids (lawn mower oil, fuel stabilizer, etc) specific to your engine.
- Find the right spark plug(s) & adjust gap settings.
- Disconnect the plug lead and remove with a spark plug socket.
- Replace with your new plug, taking care not to over-tighten (15 ft. lbs. / 180 in. lbs. (20.3 Nm)) and re-attach the spark plug lead.
Still have questions? Find more tips for troubleshooting lawn mower engine problems, check out our full list of Frequently Asked Question on Repairing Small Engines or contact a Briggs & Stratton service dealer near you.