The spark plug is one of the most critical components of any engine including motorcycle engines. It also can tell you very much about the inner working of your engine.
The spark plug is what ignites the air/fuel mixture in the cylinder at the top of the compression stroke of the engine. Simply stated it keeps the fire alive in your engine. By analyzing the condition of your spark plug you can determine if other issues are present in your engine.
Below are a variety of conditions that you can determine after you have properly removed the spark plug from your engine. Be sure to check all of your spark plugs as each cylinder may have its own unique condition. Recently I was able to determine that I had a bad jet in my carburetor as one of my spark plugs was indicating that I was getting too much fuel into the cylinder creating what is referred to as a “too rich” condition.
Spark Plug Condition Types
Too Rich – The spark plug looks black and is wet to the touch, this is an indication that there is too much fuel in the air/fuel mixture
Too Dry – This condition can be harder to determine as it looks closer to what a normal spark plug should look like, but if you notice a high amount of black carbon dust on the spark plug where you can no longer see the white core of the spark plug and any exposed metal then this indicated that there is not enough fuel in the air/fuel mixture.
Normal – The spark plug should look closer to a brand new spark plug, a small amount of carbon buildup and blackening is normal over time.
Overheating – If the metal starts to become glazed and distorted in shape almost looks like it has been melted it is a sign of the engine overheating.
Spark Plug Damage – If the core of the spark plug appears to be broken off it can be caused by excessive expansion of contraction of the spark plug itself. This can be caused if the motorcycle is not properly warmed long enough and heats or cools too rapidly. If the ground electrode is broken off it can be caused by improper cylinder clearance or excessive corrosion caused by water, lead, or another fluid in the cylinder.
If you bring your spark plug to any trained mechanic they should be able to reconfirm your findings or offer you even more detailed information about the current condition of your engine. It may be worth the effort as a proper diagnosis will save you much time from trying to fix an engine component that may not need to be fixed.