Basic Maintenance Procedures
Spark Plug Maintenance (cont.)
Normal Spark Plug
(light brown center)
Lean Spark Plug
(White center)
Fouled Spark Plug
(Heavy carbon buildup)
Fouled Spark Plug
(Heavy oil buildup)
Side Electrode
Insulator
Threads
Spark Plug
Gap
Center Electrode
A fouled (dirty) spark plug can cause your motorcycle to run
poorly and lose performance. Follow the steps below to
inspect, clean and/or replace the speark plug if needed.
1. Clean any dust and dirt from around the spark plug base.
2. Disconnect the spark plug cap.
3. Remove the spark plug using a 5/8 in socket or wrench.
4. Using the photos below for reference, examine the plug
to determine it’s cleanliness.
If the plug is a normal
color, go on to step 6. If the plug is fouled (dirty), go to
step 5.
5. Using a moderate grit sandpaper (220-400), sand
between the center electrode and the side electrode
until all carbon and oil deposits are removed. Monster
Moto recommends that you use a spark plug cleaner
or a new spark plug if the plug is very dirty.
6. Inspect the spark plug electrodes for wear. The center electrode should have square edges. The
side electrode should not be eroded at all. The insulator should not be cracked or chipped.
Replace the plug if any electrode wear and/or cracks are present.
7. Check the spark plug gap using a spark plug gapper. Gappers can be purchased at your local auto
parts store. The spark plug gap should be .02 - .03 in (0.6 - 0.7mm). Always check the gap of a
new spark plug before you install it. 8. Be sure all dirt has been cleaned from the threads. Install
the spark plug by hand. This will prevent stripping and/or cross threading of the threads. Use a
5/8 in socket or wrench to securely tighten the spark plug. Do not over or under tighten the spark
plug.
Notice: Improperly tightened spark plugs can damage the engine. Too loose, you can burn a hole in
the piston. Too tight, you can damage the threads of the engine.
When you inspect the spark plug, generally it will fit into one of the four categories shown above. A
normal/clean spark plug will have a light brown center and displays no wear around the electrodes. A spark
plug with a bright white center indicates a lean condition in the engine. If your plug looks like this, have
your motorcycle serviced by your Monster Moto dealer immediately. A carbon fouled plug will be completely
black with no gloss. An oil fouled plug will appear a dark shiny brown or shiny black as shown above. An
oil fouled plug is caused when the engine oil seeps by the piston ring and is burned with the fuel. Oil fouled
plugs are not uncommon, however, if your motorcycle is consistently oil fouling spark plugs, have it serviced
by your local Monster Moto dealer immediately.
23 Maintaining Your Dirtbike
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