How To Change a Spark Plug on a Dirt Bike

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A hand holding a wrench and opening the spark plug on a dirt bike

As much as we’d love to be riding dirt bikes all the time, some maintenance days need to be thrown in every now and then. Today, it’s time to change the spark plug.

Changing the spark plug on a dirt bike usually requires removing the gas tank, disconnecting the spark plug lead, and replacing the old spark plug with a new matching spark plug. In some dirt bikes, you can replace the spark plug without removing the gas tank.

Luckily, it’s an easy job to change the spark plug on a dirt bike. Especially, if you follow these easy five-step instructions. Let’s get started!

Why and When To Change the Spark Plug

The spark plug gets contaminated over time. The carbon build-up may cause a weak spark resulting into rough idling or having difficulties with cold starts.

Changing the spark plug on a dirt bike is part of the regular bike maintenance and recommended every 40 hours of riding or so. If your bike is running rough, sputtering, or losing power already before that, you should examine and change the spark plug if necessary.

Changing the spark plug will take you about 15 minutes. Time spent on the task varies depending on how easily you can access the top of the cylinder head area with tools. The only tools you will need are regular maintenance tools that usually come with the dirt bike tool kit.

Read also: How To Flush Radiator Coolant on a Dirt Bike

Step 1: Clear Space To Access the Cylinder Head Area

Changing the spark plug on most dirt bikes can be performed with the gas tank on. However, getting your wrench fit well might be an issue.

Read also: How To Remove The Gas Tank On A Dirt Bike

The multi wrench that comes with many dirt bike toolkits should fit and have enough space to open the spark plug and retighten it safely. This works great when you need to change the spark plug trailside. But we recommend performing the spark plug swap at the same time with other maintenance tasks while you have the gas tank off the dirt bike.

A dirt bike standing on a center stand with the seat, gas tank and plastics removed
The gas tank, side plastic panels, and head exhaust pipe are removed for clear access to the cylinder head.

Having said that, let’s start by removing the gas tank and the plastics that are holding the gas tank in place. You want a clear access to the cylinder head and to be able to have enough space for the wrench to fit well.

Step 2: Remove the Spark Plug Cap

Remove the rubber spark plug cap by grabbing it tightly and pulling it straight upwards. You can wiggle it if it appears to be stuck.

Once it comes loose, do not twist or pull the cap as it may disconnect from the lead wire and cause a weak or lost spark. Set it aside away from the spark plug. You can use a zip tie if needed to keep it out of the way.

If you have intermitted issues with the dirt bike and you suspect it might be related to ignition issues, check the spark plug lead wire thoroughly. Sometimes the plug may become loose from the lead wire and may cause a weak spark. To make sure it’s not loose, rotate the black rubber lead connector clockwise while pushing it inwards into the lead wire.

Step 3: Remove the Old Spark Plug

Use a closed-end wrench to carefully open the old spark plug by rotating counterclockwise. Once you break the spark plug loose, use your fingers to thread the old spark plug out.

Hands holding a wrench around a white spark plug on a dirt bike cylinder head and about to change the spark plug

The spark plug usually has a rubber seal preventing dirt build-up around the spark plug. You need to save it and reuse it on the new spark plug.

Step 4: Change the Spark Plug Into a Matching Plug

Next, compare and make sure the new spark plug has the matching temperature setting and size as the old one. The text on the spark plug isolator, that is the white part, indicates the spark plug heat setting and they need to match.

Check your owners manual for the original recommended spark plug model.

Dirt Bike Spark Plug
NGK Offroad Spark Plug
$20.45
A white spark plug threaded slightly in on a dirt bike cylinder head

Move the rubber seal or grommet from the old plug to the new plug. Thread the spark plug back in place by hand all the way in first.

Then snug it slightly with the wrench. DO NOT OVERTIGHTEN. A good thumb rule is to tighten the spark plug in by hand, then use the wrench and turn ONLY 1/8 of a turn.

Reinstall the spark plug cap by holding it tightly and pushing it straight down. You should hear an audible click and feel when the plug cap is in place.

Make sure the cap wiring is unobstructed and clear of the gas tank mounting areas. Use zip ties if necessary to fix it in a stable position.

Step 5: Finish the Gas Tank Assembly

Reinstall the gas tank and side plastic panels to finish the spark plug change.

When installing the gas tank, check that the spark plug lead wire and the throttle cable are not crimping under the gas tank mounting points. Sometimes there is not a lot of space between the gas tank and the frame around the mounting points and correctly routing the wires is extremely important in order to prevent future issues.

Read also: Top End Rebuild Process On A Two-Stroke Dirt Bike

Conclusions

Change the spark plug often into a fresh one, especially with two-stroke engines. It is a quick and easy way to prevent cold starting issues and resolve a rough idle.

Spark plugs are cheap to buy, so carry a spare one in your trail tool kit and you will be able to change the spark plug trailside should any issues occur.

Keep on firing!

Last updated: June 16th, 2022