How to change a spark plug in a lawn mower

If the spark plug in your mower has gone bad, you’ll struggle with issues like hard starts and engine misfires until you replace it.

This short guide teaches you how to change a spark plug in a lawn mower.

This shouldn’t take you long even if your mechanical skills are wanting.

Read on.

What you need (tools and equipment)

  • Lawn mower spark plug socket/spark plug wrench.
  • A wire brush.
  • Spark plug gauge (or feeler gauge) or even fine gap checker.
  • Knife.
  • Replacement spark plug.
  • Spray-on plug cleaner.

Preliminaries

How to change a spark plug in a lawn mower: step-by-step

Let’s look at how to remove the current spark plug first.

Stage 1: Removing the old spark plug

  1. Start by disconnecting the old/worn spark plug lead/wire. In most cases, the spark plug is on the front (though it can also be on the side) of the mower.

Tip: Refer to your owner’s manual if unsure about the location of the spark plug in your mower.

Note: You may have to remove the mower engine cover (if equipped with one) to see the spark plug wire.

  • At this point, best practice dictates that you clean the area surrounding the spark plug- you don’t want the debris to find its way into the combustion chamber later after removing the plug.
  • Fit your spark plug socket/spark plug wrench over the plug.
  • Now turn it counterclockwise gently and carefully until you get the plug out.

Tips:

  • Prior to moving on, it’s good to be sure that your plug needs to be changed since it’s not always the case. Observe it keenly and look for signs of being burned, fouled, cracked, or eroded.
  • We recommend that you wipe the deposits from the spark plug using a wire brush and the spray-on plug cleaner to get a clear view. Use a sturdy knife to scrape off stubborn deposits.
  • In the absence of the aforementioned signs, it’s safe to reinstall the old plug. Otherwise, proceed with the replacement.

Note: Whether reinstalling the existing plug or fixing a brand new spark plug, the next steps are similar.

Stage 2: Fitting the new spark plug

  1. Using the spark plug gauge, measure and set the correct gap between the center and ground electrodes (at the tip of the spark plug).

Here is the thing: Many mowers require a 0.030 inch gap but you should follow the specific measurement for your model.

Tip: Go back to your owner’s manual to check the correct gap if lost. 

  • In case of an inaccurate gap (maybe it’s higher than specified), try to modify it by tapping the curved electrode gently until you get the correct measurement.
  • Finally, we come to installing the plug, which is pretty straightforward- you do the reverse of the removal process as described in step 4.
  • Simply screw in your new plug then tighten it with your spark plug wrench. Avoid over-tightening the plug as doing so could easily distort the plug among other potential problems.
  • Re-attach the spark plug wire/lead and mount the engine cover where necessary.
  • Start the lawn mower. Everything should run smoothly if you followed the above steps correctly.

Tip: If upon starting it you experience problems such as the engine trying to turn over then dying, it could signal that the trouble likely lies in other parts (the carb, ignition system, etc.).

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When to tell if it’s time to change the spark plug in a lawn mower

 So, how do you tell if it’s the right time to change the spark plug in your mowing machine?

Well, a couple of symptoms should give you pointers that your spark plug is no longer supporting the mower’s combustion system as it should and it needs to be replaced.

Here they’re:

  • Lawn mower wont start – for a lot of people, this is the clearest sign that you’re stuck with a bad plug. Be on the lookout for difficult than normal starts.
  • Excessive fuel consumption- if your mowing monster has suddenly become fuel-hungry and you have to refill it more times than you’re used to when cutting, inspect the condition of your spark plug.
  • Persistent engine problems- the engine may be starting- though after a lot of hassle- but then it really becomes a bother and you cannot mow in peace. For example, it dies out immediately. It could also run for a few minutes then stop. Faulty spark plugs also cause the engine to misfire as mentioned earlier.

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Tip: Like other small engine maintenance, manufacturers have different recommendations when it comes to the spark plug. Most, however, suggest that you should physically inspect and change the spark plug annually. As always, don’t wait -check and change the spark plug according to the timings printed in your operator’s manual.

A word on the replacement plug

Overall, lawn mower spark plugs are not that expensive and it’s best to replace them with a manufacturer-endorsed model.

Consult your operator’s manual for the spark plug that corresponds to your mower’s make and model.

You can also enquire from the dealer/manufacturer via phone or the website.

Another solution could be to go for the same plug you have in your mower currently.

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How to change a spark plug in a lawn mower: frequently asked questions (FAQs)

How long should a lawn mower spark plug last?

According to experts, a mower’s spark plug should be changed once a year assuming that you take good care of the machine.
That said, most owners find it wise to replace the spark plug once per season.
Manufacturers such as Briggs and Stratton are more specific and recommend that you change the plug after cutting with it for about 25 hours.

How can I pull a stubborn spark plug out?

You should never use a lot of force when trying to get a stuck spark plug out.
The best option is to spray some penetrating oil all around the base and let it sit for about 10 minutes.
You can then retry to pull it out with a spark plug wrench/socket.

Conclusion

Changing your mower’s spark plug when due will go a long way in maintaining its peak performance, smooth operation, and excellent gas mileage.

You now know how to change a spark plug in a lawn mower so we expect that you’ll have little trouble completing this important maintenance chore.

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