Lawn Mower Spark Plug FAQ: 14 Things to Know

The spark plug is a small metal part that sits in the center of the engine and sends an electric jolt to ignite fuel. It’s responsible for turning gasoline into power, so you can start your lawn mower and cut grass – without it, you’re dead in the water.

With all these parts working together to make something happen, it might seem like there are a lot of questions about how spark plugs work. And sure enough: 14 things to know about this tiny but mighty component!

Are All Lawn Mower Spark Plugs the Same?

Unfortunately, there are no universal spark plugs for mowers and nearly all manufacturers have selected their own size specifications and standards for use with their motors. A majority of lawn mower spark plugs are somewhere between 10-12mm in terms of thread size.

Automotive spark plugs are usually sized around 14mm, so you can’t use these either.

How Do I Know if My Lawn Mower Spark Plug is Bad?

In many cases, your mower simply won’t start. You might also have a bad spark plug if you have to tug extremely hard on the rope to get it to start.

Riding mowers with bad spark plugs might not turn over at all.

What Spark Plug Does My Lawn Mower Use?

While it’s hardly ideal, every lawnmower manufacturers has more or less elected to use their own sizes. If you don’t know what kind of plugs you have, then you’ll usually find printed dimensions on the side of the physical plug.

Threads for spark plugs are measured in millimetres in terms of three different dimensions. You’ll need to know the reach, pitch and diameter to pick a new replacement plug.

Are Spark Plugs Universal for Lawn Mowers?

Lawnmower spark plugs aren’t universal. Sometimes, motors made by the same company won’t even use the same spark plugs.

Fortunately, spark plugs usually have their dimensions written on them. You can measure the spark plug’s metrics simply by taking out a ruler, but this usually shouldn’t be necessary.

What Happens if You Use the Wrong Spark Plug in a Lawn Mower?

It usually just won’t fit because spark plugs are carefully sized to fit in a specific slot. Even if it does, it’s highly unlikely that the gap would reach high enough to fire.

It can be extremely unsafe to use poorly sized plugs, so you’re highly discouraged from doing so.

When Should I Change My Lawn Mower Spark Plug?

Both push and riding lawnmowers should have their spark plugs changed every 100-150 hours of continuous usage. That usually translates into around 2-3 years for residential users.

Commercial landscapers may have to change their spark plugs much more frequently if they cut a lot of lawns.

Can You Clean Spark Plugs With WD40?

You can clean spark plugs with WD40, but you have to disconnect them first and spray the WD40 into a clean rag. Wipe the grime off of the spark plug and then dry off any excess before putting it back into the hole so none of the solvent gets stuck down there.

WD40 can also be used to remove corrosion from not only the spark plug but also many other components attached to your lawnmower.

Can a Lawn Mower Start Without a Spark Plug?

No, a gas-powered lawnmower needs some form of spark to start, so it couldn’t start without one. Battery-powered electric lawnmowers don’t need spark plugs, however, and can start just fine without them.

Though you can probably start a lawnmower with an old or damaged plug, you should really replace these as well because they can severely hamper fuel economy.

What is the Difference Between Rc12yc and Rc14yc Spark Plug?

Champion makes both of these spark plugs, and they really only differ in the size of the spark gap. The Rc12yc has a .020 gap and then hotter Rc14yc plug has a .040 gap.

Though they’re probably just around the same size, you don’t want to experiment with them too much because the Rc14yc could generate too much spark for some smaller types of motors.

What Can I Use to Clean My Spark Plugs?

The best way is to use a commercial spark plug cleaner, which sandblasts the plugs to like-new condition. Unfortunately, these are becoming really hard to find since so many just buy new spark plugs to replace their dirty ones.

Sometimes, you can use a dry shop towel to simply wipe the spark plug clean. A little WD40 or dedicated automotive brake cleaning solution can help quite a bit.

How Do You Clean Dirty Spark Plug Wells?

Put some carb cleaner on a clean shop towel or rag and then gently push it down the well with a screwdriver. You should be able to then remove the rag quickly and pull out a good amount of the grime with it.

Don’t pour anything else down the well. If this hasn’t cleaned it, then just push the rag down the well again and see what you can get out.

How Do You Gap a Spark Plug Without a Tool?

Most modern lawnmower spark plugs come pre-gapped, so you might be able to push it into the slot without using any tools. If you have any reason to think that the preset gapping is off, then you can usually use a dime or a penny to adjust it slightly simply by putting said coin underneath the spark plug’s head.

What Is an Eco Spark Plug?

Eco spark plugs are premium small engine plugs from Champion that are designed to improve fuel economy. They cost more than regular spark plugs, but many users say that they pay for themselves by saving on gasoline.

Those who are concerned about their lawnmower’s emission profile might also want to give these a try. They’re usually offered in the same sizes that most people would expect for their motors, but you’ll need to check because every engine manufacturer is different.

How to Change a Lawn Mower Spark Plug

Changing a lawnmower spark plug is usually as easy as removing the current connector, extracting the plug with your fingers by twisting it and then pulling it straight out. Twist the new plug in, spark igniter side up, and replace the wire connector.

You should then be able to start your lawnmower again like normal. Never yank the wire itself, however, because you can easily damage it.