Best Spark Plugs for Lawn Mowers: Which One Fits the Way You Use It?

Best for most push mowers: the Briggs and Stratton 491055 spark plug two pack, around $7, replaces the common Champion RC12Y style plug used on many Briggs and Stratton engines.

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Best for OHV engines: the Briggs and Stratton 496018 spark plug two pack, around $6, is made for overhead valve engines and replaces 5066K and RC14YC plugs.

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Best tune up kit: the Honda Lawn Mower Tune Up Kit, around $24, is built for Honda GCV and GC series engines and includes a spark plug, air filter and related parts for a complete seasonal service.

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Here is how to match the plug to your situation.

For Weekend Homeowners

If you mow a typical yard once a week, a standard copper core plug matched to your engine is all you need. Buy a two pack so you have a spare, and replace the plug once a season or every 25 to 50 hours of use. Look up the correct part number in your manual or on the engine label.

For Owners of Several Machines

If you maintain a push mower, a riding mower and other small engines, check which ones share the same plug and buy a multipack. Many Briggs and Stratton, Kohler and Champion powered machines use a few common plug types, and bulk packs cost less per plug.

For Frequent or Serious Users

Large property owners and people who mow several times a week should replace plugs more often and consider a full tune up kit each season. A kit with a plug, air filter and oil keeps the engine running cleanly and makes service quick.

For Dusty or Tough Conditions

Dry, dusty mowing and tall grass make engines work harder and can foul plugs sooner. Check the plug more often, keep the air filter clean and carry a spare plug and socket in the shed.

These are the details that matter when buying a mower plug.

Correct Fit for Your Engine

The most important factor is matching your engine's specified plug. Thread size, reach and heat range must be correct; the wrong plug can run poorly or even damage the engine. Cross reference charts help if your manual lists another brand's part number.

Heat Range

Heat range describes how quickly a plug sheds heat. Engine makers choose the right range for their design, so stick to the recommended plug rather than guessing.

Electrode Material

Most mower engines use copper core plugs, which are affordable and work well. Platinum and iridium plugs last longer in cars, but most small engine makers specify copper, and the extra cost rarely pays off on a mower.

Gap

The gap between electrodes must match your engine specification, often around 0.020 to 0.030 inches for small engines. Check it with a gap gauge before installing, since plugs are not always pre gapped for your engine.

Pack Size and Kits

Single plugs suit one mower, two packs give you a spare and bulk packs suit several machines. Tune up kits bundle the plug with an air filter and oil for a full service.

1. Make sure the engine is cool, then pull off the spark plug wire.
2. Clean around the plug so dirt does not fall into the cylinder.
3. Remove the old plug with a spark plug socket, turning counterclockwise.
4. Check the gap on the new plug and adjust it if needed.
5. Thread the new plug in by hand, then snug it with the socket, usually about a half turn past finger tight for a new plug with a gasket.
6. Reattach the wire and start the mower.

• Guessing the part number instead of checking the manual or engine label.
• Skipping the gap check before installing.
• Overtightening, which can strip aluminum cylinder head threads.
• Replacing only the plug when the air filter is clogged too.
• Paying for iridium when the engine maker specifies copper.

• Inspect the plug each spring; black soot or oily deposits signal other engine issues.
• Replace the plug yearly or every 25 to 50 hours.
• Keep blades sharp so the engine does not strain.
• Use fresh fuel and stabilizer for winter storage.

These are the questions mower owners ask most.

How do I know which spark plug my lawn mower needs?

Check the owner's manual or the engine label for the model number, then look up the specified plug. You can also read the part number on the old plug and use a cross reference chart.

How long does a lawn mower spark plug last?

Most last one mowing season, or about 25 to 50 hours. Replace it sooner if the mower is hard to start or runs rough.

Can a bad spark plug stop a mower from starting?

Yes. A fouled, cracked or worn plug is a common cause of hard starting. Old fuel and a dirty air filter are other common culprits.

Are all lawn mower spark plugs the same?

No. Thread size, reach and heat range vary by engine, so always match the plug to your engine.

Should I gap a new spark plug?

Yes. Check the gap against your engine specification with a gauge before installing, even if the plug says pre gapped.

The three things that matter most are matching your engine's specified plug, setting the correct gap and replacing it every season. Weekend mowers need a simple two pack, owners of several machines save with multipacks and frequent users benefit from full tune up kits. Use this guide to choose the best spark plugs for lawn mowers, then check the product table above for current prices. Finish your service with the best oil for lawn mowers.