Spark plugs are the most essential part of your motorcycle’s ignition system. Yet, for many riders, there’s a sense of mystery to them. It’s easy to take spark plugs for granted until there’s a problem, but there are things every rider should know about these fundamental components of your bike. What are the bad spark plug symptoms that are common on a motorcycle? What are the signs that it’s time to change a motorcycle spark plug? What is the plug gap, and why is it significant? This Taverner Motorsports guide to checking, maintaining and changing your motorcycle spark plugs will provide answers to these questions and help even the least DIY-inclined rider understand more about spark plugs.

Located in your internal combustion engine, spark plugs produce the sparks that light the mixture of air and fuel inside the chamber. An engine’s ignition coil sends high-voltage electricity to the plug and creates a spark in the small gap between electrodes. Spark plugs vary in size, but all of them are actually made up of smaller parts, including the terminal nut, gasket, middle shell and centre electrode. But while spark plugs are more complex than meets the eye, taking care of them is relatively simple. Read on to get the rundown on how to check, adjust, replace and clean the spark plugs in your motorcycle.

How to Check Your Motorcycle Spark Plugs

Spark plugs take a lot of heat and put up with a lot of pressure. Luckily, they’re tough, but don’t let that make you complacent. There’s a reason a lot of motorcycle mechanics replace the spark plugs even on minor services. These little guys have a big job to do, and when even a single one of them isn’t up to the job, it can wreck your whole ride.

Luckily you can check your motorcycle spark plugs yourself and even change your motorcycle spark plugs using tools such as torque wrenches and plug gauges.

Checking your spark plugs gives you a good indication of what kind of condition your engine is in. Your spark plugs are usually located on the top of the engine under rubber boots connected to black wires. To read a spark plug, you need to remove it and have a look at the firing end: the end that goes inside the engine. A healthy spark plug has a tan, brown or grey firing end, indicating that both the plug and the engine are working as they should. If the spark plug has an unusual appearance (more on that below), that’s a sign of a problem with the plug, engine or fuel system. It also means you’re more likely to experience bad spark plug-related symptoms with your motorcycle.

Motorcycle Spark Plug Health Guide

Your spark plugs should be tan, brown or grey on the firing end. Issues with your spark plug or engine usually result in the following changes and discolourations. If you have any of these issues, it’s likely that you also have bad spark plug-related symptoms in your motorcycle. 

Deposits of light brown ash

Light brown ash flecks on the insulator and electrodes are usually caused by oil in the combustion chamber and can lead to engine misfires.

Deposits of dry black carbon

Generally caused by a fuel mixture that’s overly rich, these black carbon deposits lead to weak sparks and engine misfires.

Wet spark plugs

If your spark plugs are wet or oily, this indicates issues with the valve train or water in the spark plug. These issues often lead to misfires when attempting to start the engine.


An overheated spark plug tends to have a “polished” appearance, which is usually the result of using a loose or incorrect plug in the wrong temperature range.


When you look at a spark plug, there are few sights more alarming than seeing it melting away. A melted spark plug’s dramatic appearance is caused by your engine overheating at a very high temperature. You may also notice blisters and white spots on the plug.

These are just some of the most common signs that it’s time to clean or change your motorcycle spark plugs. If you notice any strange changes in appearance or rough riding, it’s worth getting to the bottom of it with a professional.

Motorcycle Spark Plug Maintenance

When it comes to your bike’s spark plugs, a little maintenance goes a long way. That includes cleaning the spark plugs on your motorcycle, adjusting them or changing a motorcycle spark plug if necessary.


Before you clean the spark plugs on your motorcycle, make sure you have tools such as screwdrivers, spark plug sockets, a cleaning brush (an old toothbrush will do) and a cleaning agent like WD-40 at the ready. Open the cover on the left-hand side. Remove the spark plug cap and avoid touching the engine if it’s hot. Use the socket to open the spark plug and check if it’s been affected by carbon or rust. Use your cleaning agent and brush to get the spark plug clean, and then reverse the steps to reinstall it.


Gapping a motorcycle spark plug involves setting the gap between the centre and ground electrodes so that your engine can function correctly. It’s important to get the gap right: you need a gap large enough to allow room for a massive spark but not so large that the ignition parts need to work extra hard. If you don’t know what your optimal spark plug gap is by heart, it’s best to consult your manual. A simple gapping tool that looks like a coin is often all you need to adjust the gap.


To change your motorcycle spark plugs, remove any motorcycle parts, such as the seat or tank, that are in the way. Remove the wiring from the plugs one at a time to avoid getting them mixed up. A cracked or broken insulator requires replacing, while a qualified mechanic’s opinion is best for any kind of heavy build-up. You can use a tool like a brass brush for any deposits you can clean off yourself.

Motorcycle Servicing at Taverner Motorsports

If you’re having bad spark plug-related symptoms with your motorcycle, like misfiring, backfiring, overheating or strange-smelling gas, there’s a very high chance it’s time to change your motorcycle spark plugs.

Taverner Motorsports provides regular motorbike servicing in order to keep your bike running smoothly and in amazing condition. We also offer minor services between the major ones to keep your bike healthy and prevent problems. During both servicing options, we change your motorcycle spark plugs and other essential components. 

Taverner Motorsports has been in the motorcycle business since 1975. We’ve worked on all kinds of motorcycles and have done everything from changing spark plugs to undertaking basic repairs to building custom creations from scratch. Over the decades, we’ve built relationships with partners and parts suppliers both locally and around the world. Everyone who works at Taverner is as passionate about motorcycles as you are, and when you bring your motorcycle to our workshop, we’ll treat it with the same level of care as one of our own.

For more information about our motorcycle servicing options and other services like restoration, customisations and modifications, contact the Taverner team and request a quote.