How to Read Spark Plugs

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 just 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 is what usually leads to procrastinating it. It is a lot easier to do this on a 2-stroke bike 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 is going to prevent any potential no-starts.

It is also advisable to keep the tools necessary for changing your spark plug. If you have a spark plug removal tool, it is going to serve you a lot better 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 ratio and the gas ratio are too high, which implies that it is too high for a proper mix, which does not allow for the 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 quality of oil, as prescribed by the riders’ manual. 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 to 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 to 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 are going to be able to anticipate problems well in advance and prevent any long-term damage to the engine. It is advisable to read the spark plug regularly, 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 take out 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.

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