Spark plugs.

How to read a spark plug

Examining your engine’s spark plugs can give you an idea of how the engine is running. You can do this as part of the routine maintenance of your motorbike or if you suspect something is wrong with the engine.

Getting Started

The first step is removing the spark plug you want to look at. Take the spark plug in your hand and begin looking at it for signs of damage. Look at end of the spark plug that was in the cylinder and examine it. You will likely see one of the following conditions.

Normal spark plug

A normal spark plug will have brown or grayish-tan deposits on the side electrode. Everything is just fine with your spark plug; you can reinstall the spark plug.

Carbon fouled

Black, dry soot on the electrodes and insulator tip indicates a carbon-fouled plug. This can be caused by a dirty air filter, excessive driving at low speeds, too rich of a fuel/air mixture or idling your vehicle for too long. You may want to consider switching to  a “hotter” spark plug (the higher the spark plug number, the hotter the plug).

Oil deposits

Black, oily deposits on the electrodes and insulator tip points to an oil-fouled plug. Oil could be leaking into the cylinders, getting past pistons that are worn or valve guides that are worn.  Finding the source of the leak is very important. Once the problem is addressed, you can replace the spark plug.

Wet

A wet spark plug can be the result of the engine flooding. Flooding is what happens when you try to start the engine several times without it firing up. You can clean the spark plugs or you can just wait for them to dry out.

Burned

Blisters on the insulator tip, melted electrodes, or white deposits are signs of a burned spark plug that is running too hot. Causes can include the engine overheating, incorrect spark plug heat range, a loose spark plug, incorrect ignition timing or too lean of an air/fuel mixture. The spark plug should be replaced.

Worn electrodes

Worn and eroded electrodes are symptoms of a spark plug that is past its prime. The plug has been in the engine too long and needs to be replaced.

Broken electrodes

If the electrodes are broken off or flattened, it is likely that the wrong spark plugs are installed.  A spark plug that is too long can cause extensive damage to your engine while a short spark plug can cause poor MPG and spark plug fouling. Check your owner’s manual to ensure that you have the correct spark plug for your vehicle.

Cleaning spark plugs

Ultimately, you won’t get the same performance from a cleaned plug as from a new plug. Electricity discharges best from sharp edges. A used plug will have worn edges, and cleaning may contribute to the wearing.

If you insist on trying to clean anyways, the cleaning procedure below was supplied to us by an old motorhead:

• Brush off the plug and firing tip with a clean rag.
• Spray the firing end with a quick-dry cleaner such as fuel injector cleaner or brake cleaner. Let sit 10 minutes.
• Use a wire brush to clean off any deposits that have loosened.
• Blow off the plug and firing end with an air compressor or can of compressed.
• Re-gap to your vehicles specifications using a feeler gauge.
• If the plug has a flat seat, remember to use a fresh gasket, or adjust the installation torque accordingly.

Alternatively, you can buy a pneumatic spark plug cleaning tool to use with a compressor, it is like a mini sand blaster, this will only really work on fouled plugs.

NOTE: Insufficient cleaning of a spark plug may lead to its failure in a very short period of time. Clean the spark plug thoroughly to avoid problems later. Remember, if a plug is fouling, its usually a result of engine side factors or incorrect heat range selection. If, after cleaning, a plug shows unusual signs of wear or doesn’t come clean, its time to replace it.

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