Last Updated: August 15th, 2023

How to Read Spark Plugs?

Even though it might seem like the least attractive part of your ATV bike, a spark plug turns out to be the most important. The spark plug on your ATV is that part of your bike that not only keeps your engine running but also keeps it going by maintaining a continuous spark firing. 

A spark plug mostly becomes bad because of neglect.

Granted, it is difficult to check for the condition of your spark plug on a 4-stroke bike because it involves removing the gas tank, which usually leads to procrastination. Doing this on a 2-stroke bike is a lot easier because it sits right at the top of the cylinder head. 

The other thing about this is that if you are on a 4-stroke, then you would ideally need a six-to-eight-inch socket extension, whereas, on a 2-stroke bike, you can easily get the job done with an open wrench. 

ATV spark plugs come in different price ranges, and they can cost as little as $4 to $50, depending on the type of spark plug that you are going for.

It is important to note that spark plugs usually last longer on 4-strokes, which doesn’t discount a regular visual check. This is going to prevent any kind of no-start down the line. Having a regular maintenance routine in place will prevent any potential no-starts.

Keeping the tools necessary for changing your spark plug is also advisable. If you have a spark plug removal tool, it will better serve you in emergencies.

How To Read Spark Plugs?

Removing a spark plug

This process is fairly simple and should be followed, as mentioned here. Pull off the cap and remove the wire that is in place. Use the socket wrench or the open-ended wrench to remove the spark plug. This is the safest and most efficient way of removing the spark plug.

Replace the existing one with the new spark plug, and ensure that you align the threads properly before tightening and finishing. This is because if you don’t do this, you are going to end up like a lot of ATV riders who over-tighten the spark plug and then munch it off inside the cylinder head. 

If you do not want to deter yourself from ever touching a spark plug again, we would advise you not to do this. The wisest thing to do in this situation would be to take a torque wrench and tighten the spark plug inside. 

How to read a spark plug color

Knowing how to read a spark plug can be an extremely useful tuning aid. This is because by examining the spark plug insulator’s color, you will easily be able to evaluate the working condition of the engine. 

Normal and Working fine:

If the spark plug insulator is a grey or a light golden-brown color, then this means that your engine is in proper working condition and the air/fuel mixture is working properly. 


Your spark plug insulator will mostly read a black sooty sort of color, primarily because the air/fuel mixture is too rich, the carburetor has not been set properly, or the flame arrestor has mounting problems.

This can also mean that the spark plug heating capacity is too cold for the existing conditions. The other scenario could be that the ignition system could be causing an irregular spark and could be spurting out fuel while not working efficiently. 

Shiny, Wet

This is a condition that is commonly referred to as wet fouling. This is usually what happens when there is excessive use of the choke.

This can also happen when there is a sustained low RPM position (this happens with a lot of 2-stroke bikes) OR if the fuel-to-oil ratio is completely off.

The oil and gas ratios are too high, implying that they are too high for a proper mix, which does not allow for an adequate amount of burning for the plug. This is usually something that you will notice more when you have been driving around in the city or on highways. 

Chalky, Bumpy Build-up

When this happens, it means that there are excess deposits. This is usually an indication of a bad fuel problem.

It is imperative to ensure that you are using the right oil quality, as the riders’ manual prescribes. If you can rule that out as the problem, then the next best thing for you to do would be to look at the combustion chamber. 


If you see a sparkly white color reading of your spark plug and if it is blistering, your plugs are likely overheating.

The first place to go will be to check if this is an air or fuel problem, i.e., if it is set too lean. If that is not the case, then it could definitely be a torque problem. If it is neither of these two, then the last place to go would be to check the timing, just in case their speed has caused the spark plugs to burn out. 

If you learn how to read spark plug colors, you can anticipate problems well in advance and prevent any long-term damage to the engine. Reading the spark plug regularly is advisable, which would mean once every two months. 

The best way to read your spark plug color is by driving the ATV to its last gear, pulling full throttle, and hitting the clutch lever. Turn off the engine and remove your spark plug to see its color. 

If it is any of the colors that we have mentioned above, that means it needs replacement.

If it is a coffee milk color, that means that your spark plug is in optimal condition and doesn’t require replacement. This means that the fuel/air mixture that the bike is supposed to get is being received. Any other color other than that means that the spark plug needs checking and, in some cases, replacement.

Before you do this, read the spark plug to understand fully whether it needs fixing or a complete replacement. It’s better to see if the problem is fixable before getting into the habit of replacing your spark plug every other week.

What is the primary purpose of reading spark plugs?

Reading spark plugs helps in diagnosing the condition of the engine. By examining the color, deposits, and wear on the spark plug, one can determine if the engine is running rich, lean, or has other issues like preignition or detonation.

How does the color of the ground strap on a spark plug indicate its heat range?

The color change on the ground strap of the spark plug indicates its heat range. The heat range is too cold if the color changes too close to the strap’s end. The heat range is too hot if the color changes near where it’s attached to the base ring. Ideally, the color change should be halfway on the strap.

Why is the base ring of the spark plug important for determining jetting or air/fuel mixture?

The base ring of the spark plug shows the air/fuel mixture ratio. A full turn of light soot color on the base ring indicates an optimal mixture. If spots of heavy dry soot are on top of the color, it suggests the jetting is too rich.

What signs on the porcelain of a spark plug indicate preignition or detonation?

The porcelain of the spark plug can show signs of preignition or detonation. Early signs include tiny black specks or shiny specks of aluminum fused to the porcelain. As detonation progresses, pieces of the porcelain may break off, indicating more severe detonation.

What modifications are made to racing ATVs in terms of their spark plugs?

Unlike many basic ATVs in the market, racing ATVs might have spark plugs without speed limiters. They might also have modified suspensions and different tire widths. The spark plugs in racing ATVs are chosen to handle the higher performance demands of racing.

Why is it essential to inspect the spark plug’s insulator nose?

The insulator nose can provide valuable information about the engine’s combustion chamber temperatures. A white or light gray insulator indicates high temperatures, which could be due to a lean air/fuel mixture or advanced ignition timing. Conversely, a dark insulator might suggest a rich mixture or retarded ignition timing.

How can oil deposits on a spark plug affect engine performance?

Oil deposits on a spark plug can lead to misfires and reduced engine performance. These deposits can be caused by worn valve guides, seals, or piston rings, allowing oil to enter the combustion chamber.

What does a melted electrode on a spark plug signify?

A melted electrode indicates severe overheating, which can be caused by preignition. This condition is harmful and can lead to engine damage if not addressed promptly.

How can spark plug readings help in tuning an engine?

Spark plug readings can provide insights into the engine’s air/fuel mixture, ignition timing, and potential issues like detonation or preignition. Adjusting the engine based on spark plug readings can optimize performance and ensure the engine runs efficiently and safely.

What does a peppered appearance on the spark plug’s porcelain insulator suggest?

A peppered appearance on the porcelain insulator, characterized by tiny black specks, indicates mild detonation. This condition can be harmful over time and should be addressed by adjusting the air/fuel mixture or ignition timing.