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5.7 - Spark Plug

The recommended standard spark plug will work very well in most riding condition. However, if you plan on riding for extended periods of time at high speed or high engine rpm in hot climates, or plan extended riding in cold climates, a different plug may be recommended.

Use only the recommended type of spark plug.   

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 spark plug if needed.

  1. Clean any dust or dirt from around the spark plug base area thoroughly to prevent dirt from entering the cylinder.
  2. Disconnect the spark plug cap.
  3. Remove the spark plug.
  4. Using the photos below for a reference, examine the spark plug to determine its cleanliness. If the plug has a normal color, GO TO STEP 6. If the spark 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. We recommend that you use a spark plug cleaner or a new spark plug is the old spark plug is very dirty.
  6. Check the electrodes for wear or deposits, the sealing ring for damage and the insulator for cracks or chips. The center electrode should be nicely rounded or have square edges (depending on the type of spark plug you are using) the side electrode should not be eroded at all. Replace the spark plug if you detect either.
  7. Check the spark plug gap using a wire type feeler gauge. If the gap is not as specified, replace the spark plug with a new one. RECOMMENDED SPARK PLUG GAP: 0.6 – 0.7 mm (0.025 – 0.029 IN.)
  8. Be sure all dirt has been cleaned form the threads if you are using he old spark plug. Install the spark plug by hand first. This will prevent stripping and/or cross threading the threads. Use the appropriate socket or wrench to securely tighten the spark plug. Do not over or under tighten the spark plug.
  9. Tightening the spark plug:
  10. If using the old spark plug:

1/8 turn after it seats.

  1. If using a new spark plug:
  2. First, tighten the plug ½ turn after it seats.
  3. Then loosen the spark plug.
  4. Next, tighten the plug again:

      1/8 turn after it seats.

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 AJ1 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 AJ1 dealer immediately.


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