How to Gap Ignition Coil on a Lawn Mower?

The rhythmic whir of your lawnmower engine is a symphony of well-coordinated parts. The ignition coil, a crucial component in this orchestra, plays a vital role in igniting the fuel-air mixture, giving your mower the power to trim your green paradise. But what happens when this crucial piece starts to falter? When your mower sputters, coughs, or refuses to start, it might be time to investigate the health of your ignition coil.

This article will delve into the intricacies of gapping your lawnmower’s ignition coil, a crucial maintenance step that ensures optimal performance. We’ll guide you through the process, explaining what gapping is, why it’s necessary, and how to do it correctly using readily available tools. By the end of this guide, you’ll be equipped with the knowledge and confidence to tackle this task with ease, keeping your mower running smoothly and your lawn looking its best.

Understanding the Basics:

The ignition coil’s role is to transform low-voltage battery power into a high-voltage spark that ignites the fuel-air mixture in the combustion chamber. This spark is delivered to the spark plug, which then ignites the fuel, driving the engine’s pistons.

Gapping the ignition coil refers to adjusting the distance between the coil’s high-voltage terminal and the spark plug electrode. This gap is critical for generating the correct spark strength, ensuring efficient combustion. An incorrectly gapped coil can lead to a weak or inconsistent spark, causing your mower to start poorly, run roughly, or even fail to start at all.

Why is Gapping Important?

Gapping your ignition coil is essential for maintaining optimal engine performance and ensuring a healthy, long-lasting spark. Here’s why:

Optimal Spark Strength:

  • The gap between the coil terminal and the spark plug electrode dictates the strength of the spark. A properly gapped coil ensures a strong, consistent spark that reliably ignites the fuel-air mixture.
  • If the gap is too narrow, the spark may be too weak to ignite the fuel, leading to misfires and engine performance issues.
  • Conversely, a gap that’s too wide might result in an overly strong spark, potentially damaging the ignition system or causing premature wear on the spark plug.

Consistent Ignition:

  • Maintaining a consistent gap ensures reliable ignition of the fuel-air mixture, contributing to smooth engine operation and reducing the risk of engine misfires.
  • An inconsistent gap can lead to erratic spark delivery, causing your mower to sputter, hesitate, or experience unexpected power loss.

Preventing Spark Plug Damage:

  • An incorrectly gapped ignition coil can strain the spark plug, leading to premature wear or even damage.
  • A properly gapped coil protects your spark plug by ensuring that the spark is delivered efficiently and with the appropriate strength.

How to Gap the Ignition Coil: A Step-by-Step Guide

Gapping an ignition coil is a straightforward process that can be accomplished with a few basic tools.

Tools You’ll Need:

  • Spark Plug Gap Tool: This tool, often found in a multi-tool set, features various sized gauges for adjusting the spark plug gap.
  • Feeler Gauge: A feeler gauge is a thin metal blade with a precise measurement. It helps you accurately determine the gap between the coil terminal and the spark plug electrode.
  • Wrench: Choose a wrench that fits the spark plug size on your mower.
  • Gloves: Wear gloves to protect your hands from grease and dirt.

Step 1: Locate the Ignition Coil and Spark Plug:

  • Refer to your mower’s owner’s manual or consult an online resource for the precise location of the ignition coil and spark plug.
  • The ignition coil is typically mounted near the engine block and connected to the spark plug via a high-voltage wire.

Step 2: Disconnect the Spark Plug Wire:

  • Before you begin, ensure the engine is off and the ignition switch is in the “off” position.
  • Carefully disconnect the spark plug wire from the spark plug. This is usually done by pulling the wire off the spark plug terminal.

Step 3: Remove the Spark Plug:

  • Using the appropriate wrench, carefully remove the spark plug from the engine cylinder head.

Step 4: Measure the Spark Plug Gap:

  • Insert the appropriate gauge from your spark plug gap tool into the gap between the spark plug electrode and the ground electrode.
  • Note the current gap measurement. This is crucial for comparison once you’ve adjusted the gap.
  • The recommended spark plug gap for your mower will vary depending on the engine model. Consult your owner’s manual for the specific gap setting for your mower.

Step 5: Adjust the Spark Plug Gap:

  • If the current gap is different from the recommended gap, you’ll need to adjust it using the spark plug gap tool.
  • To widen the gap, carefully bend the electrode outwards using the gap tool.
  • To narrow the gap, bend the electrode inwards.
  • When adjusting the gap, be cautious not to damage the electrode.

Step 6: Re-Measure and Reinstall the Spark Plug:

  • Once you’ve adjusted the gap, re-measure it using the spark plug gap tool to ensure it matches the recommended gap.
  • When satisfied with the gap, reinstall the spark plug back into the engine cylinder head.
  • Tighten the spark plug using the wrench, but avoid over-tightening, which could damage the threads.

Step 7: Reconnect the Spark Plug Wire:

  • Carefully connect the spark plug wire back to the spark plug terminal.

Step 8: Test the Engine:

  • Start your mower and check for smooth operation and consistent running.
  • If you still experience issues, re-check the gap and ensure that the connection between the spark plug and the wire is secure.

Tips and Precautions

  • When working on your mower, always disconnect the spark plug wire before performing any maintenance.
  • Be mindful of the spark plug gap tool and handle it with care to avoid bending or damaging the electrodes.
  • For more intricate adjustments, a feeler gauge might be a more precise tool for measuring the spark plug gap.
  • If you’re unsure about gapping your ignition coil, consult a professional mechanic.


Gapping your lawnmower’s ignition coil is a simple yet crucial step in maintaining its overall performance. A properly gapped coil ensures a strong, reliable spark, leading to smooth engine operation, improved fuel efficiency, and a longer lifespan for your spark plug. By understanding the basics and following these steps, you can confidently tackle this task yourself and keep your mower running like a well-oiled machine, ready to tackle any lawn-care challenge.


What is an ignition coil and why is it important?

An ignition coil is a vital component in your lawn mower’s engine that transforms low-voltage electrical current from the battery into a high-voltage spark that ignites the fuel-air mixture in the combustion chamber. This spark is essential for starting and running the engine smoothly. When the ignition coil malfunctions, it can result in difficulty starting, misfiring, and even engine failure.

Therefore, maintaining a properly gapped ignition coil is crucial for optimal engine performance and longevity.

How often should I check and gap my ignition coil?

While there’s no strict schedule for checking and gapping the ignition coil, it’s generally recommended to do so at least once a year, especially before the mowing season starts. Additionally, if you notice any signs of engine problems like difficulty starting, misfiring, or a decrease in power, it’s a good idea to inspect and adjust the coil gap.

However, if you’ve replaced the ignition coil recently, it should already be pre-gapped by the manufacturer.

How do I know if my ignition coil needs to be gapped?

If you suspect that your ignition coil may be out of adjustment, you can perform a quick test.

Start by disconnecting the spark plug wire from the ignition coil and then place a spark plug tester or a gap gauge (if you have one) to the tip of the wire. While the engine is running, you should see a strong blue spark jump across the gap. If the spark is weak, intermittent, or absent, it’s a sign that the coil gap may need adjusting.

What tools do I need to gap my ignition coil?

Gapping an ignition coil is a straightforward process that requires minimal tools.

You will primarily need a flathead screwdriver, a gap gauge, and a wire brush. The gap gauge is essential for accurately measuring and adjusting the gap between the ignition coil’s terminals. If you don’t have a gap gauge, a thin piece of cardboard or a feeler gauge can be used as a makeshift alternative.

Can I adjust the ignition coil gap myself?

Absolutely, adjusting the ignition coil gap is a simple task that you can handle yourself. It’s a basic maintenance procedure that doesn’t require any specialized tools or knowledge.

However, if you’re unfamiliar with your lawn mower’s engine or feel uncomfortable working on mechanical components, it’s best to consult a qualified mechanic for assistance.

What happens if the ignition coil gap is too wide or too narrow?

Maintaining the correct gap between the ignition coil’s terminals is vital for optimal performance. If the gap is too wide, the spark will be weak, resulting in poor ignition and engine problems. On the other hand, a gap that’s too narrow can cause excessive wear and tear on the ignition coil, potentially leading to its premature failure.

Therefore, it’s crucial to ensure that the gap is set to the manufacturer’s specifications for optimal engine performance and lifespan.

What are some tips for gapping the ignition coil on a lawn mower?

When gapping your lawn mower’s ignition coil, here are some key points to keep in mind:

  • Always disconnect the battery before working on any electrical components, including the ignition coil. This is a crucial safety measure to prevent electrical shocks.
  • Ensure that the ignition coil is clean and free of any dirt or debris. Use a wire brush to clean the terminals and ensure proper contact.
  • Be gentle when adjusting the gap. Over-tightening or forcing the terminals can damage the ignition coil.
  • After adjusting the gap, reconnect the battery and test the engine to ensure that the coil is working properly.

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