How do I check, clean and change small engine spark plugs?

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Checking 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 pull 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.

When To Check & Replace Spark Plugs

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

How To Tell if a Spark Plug is Bad

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.

If the engine tries to turn over (even for a second) and dies, then you have spark. This would indicate the problem probably lies somewhere else (fuel, carburetor, valves, etc.). If the engine does not turn over at all, then there may be a problem with your ignition system. The first thing to do is change the spark plug.


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.

How To Clean Fouled Spark Plugs

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.

Changing Spark Plugs in Lawn Mowers, Snow Blowers & Equipment

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.

  1. Find the right spark plug(s) & adjust gap settings.
  2. Disconnect the plug lead, clean the area of the spark plug, and remove it with a spark plug socket.
  3. 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.

WARNING: Always read the engine and equipment manual(s) before starting, operating, or servicing your engine or equipment to avoid personal injury or property damage. See an authorized dealer if you are unsure of any procedure or have additional questions. Find all Engine Safety Warnings

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