ATV Spark Plug Bad? Tell-Tale Symptoms and Quick Fixes

Are you starting to notice that your ATV keeps stalling when you start the engine? Or have you seen a surge in fuel consumption and random engine misfires? These are all tell-tale signs of a bad ATV spark plug. They show that you need to visit a mechanic’s shop or replace the spark yourself. Without any further ado, today I will show you how to know when you have a bad spark plug in your ATV.

The ATV engine will idle roughly and misfire when the spark plug goes bad. The overall ATV fuel consumption will go up because the spark plug can’t get enough fuel to the engine. The best way to check if your quad’s spark plug is no longer good is to take a look at its color. A bad ATV spark plug will be dark. Even though it might still give spark, you will be able to instantly tell if it’s gone bad and might end up damaging your engine. This is why replacing bad spark plugs is a high priority.

Even though it can be annoying to deal with a bad ATV spark plug, luckily, replacing one is cheap. Spark plugs are inexpensive and you don’t need to be a mechanic to learn how to replace them. In fact, I will show you exactly how to do it.

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How Do I Know if My ATV Spark Plug is Bad?

The first symptom that your ATV spark plug has gone bad is rough engine idling. You will notice right from the moment that you start the engine that it sounds different than usual. However, the best way to know if the ATV spark plug has really gone bad is to take a closer look at it. A bad spark plug will have a darker color than regular ones. Another tell-tale sign that the spark plug needs to be replaced is having a difficult time starting the four-wheeler in the morning when the weather is cold.

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Check out the list below for the symptoms that showcase bad ATV spark plugs:

  • A weird engine idling sound (usually it sounds rough);
  • Increased fuel consumption;
  • Random engine misfires when starting the ATV;
  • The acceleration feels slower than usual;
  • It’s difficult to start the engine in cold weather.

Are you worried that the battery might be causing issues? If that is the case, you should check out this article where I present the most common bad ATV battery symptoms and how to fix them.

What Happens When You Have a Bad Spark Plug in an ATV?

An ATV that uses a bad spark plug will have a higher fuel consumption, misfires, lower acceleration, rough idling, and the engine will be harder to start in the morning. In the worst-case scenario, the bad ATV spark plug will make it impossible to start the four-wheeler. The plug will not give any sparks and therefore, starting the engine will not be possible without a replacement.

When Should I Change My ATV Spark Plug?

In general, ATV riders are advised to change the spark plug every 100 hours. Depending on how often you use the four-wheeler, you should change the spark plug every 600 miles or 6 months. If you keep the ATV stored safely during most seasons and ride it quite rare, my advice is to always check the ATV park to see if it has a dark color. If the spark plug is dark, you need to change it ASAP. If not, you can still ride it.

Sidenote: You can check the ATV owner’s manual to see the recommended time to change spark plugs.

How to Replace a Bad ATV Spark Plug

Replacing a bad ATV spark plug is much easier than you think. The spark plug is one of the cheapest parts on your ATV and learning how to replace it yourself will save you a trip to the mechanic’s shop and money. In order to make the process easier to follow and understand, I will split the ATV spark plug replacing guide in three parts. Without any further ado, let’s jump right into it.

#1 How to Remove the Spark Plug

The first step when removing the spark plug from your ATV is to use the OEM manual and determine what pieces of plastic need to be removed so that you can access the part. If you got the ATV second-hand and don’t have the owner’s manual or just forgot where it is, you can access your four-wheeler manufacturer’s website and download it as a PDF.

After figuring out what plastics need to be removed to receive access, you can go ahead and take them off. If you can’t determine what part is the spark plug, you can identify it by following the spark plug wire to the boot. The wire is colored red or blue and the spark plug will always be under the boot. Now, remove the plug by pulling it up. If the plug is hard to remove, you can try spraying some WD-40 around the area and give it a couple of minutes. The plug should come right off when you apply some force.

#2 Check to See if the Spark Plug is Bad

Since you have already removed the spark plug, you might as well check if it’s bad or not. As previously mentioned in the intro, you will be able to tell when an ATV spark plug is bad right from the first glance. It will have a darker color.

#3 How to Install the Spark Plug

Now that the bad ATV spark plug is out, it’s time to install the new one. You can insert the plug by hand and tighten it until it fits. Make sure not to over-tighten the plug because it’s made from soft metals that can break under pressure. The next step is to place the boot over the plug and snap it into position. This can be done just by pressing on the boot.

My advice is to try and start the engine before reinstalling all the plastics. If the engine starts, then you are good to go. If it doesn’t, this means that the plug was not installed properly.

Sidenote: If you have an easier time following video instructions, you can check out this YouTube video I linked below from Project Garage. The video does a great job showing how to change an ATV from scratch.

Final Words

You can tell that an ATV spark plug has gone bad when the engine idles roughly and misfires. If you remove all the plastics and access the plug, you will see that it has a darker color. This means that it needs to be replaced as soon as possible.

Bob Kelly

Hey there, my name is Bob and I've been riding ATVs, dirt bikes, and UTVs for most of my life. Going on outdoor adventures has always been my passion. I love sharing tips and tricks with beginners who are getting ready to join the world of outdoor enthusiasts. You can reach me at if you want to get in touch.

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