Carburetor Adjustments & Tuning Tips
126 Adjustments for Competition
Spark Plug Reading
Refer to Spark Plug on page 54.
Check any jetting change by reading the spark
plug. The following procedure is recommended.
You may not get an accurate reading if you
simply turn off the engine and pull the plug for
inspection.
Use a new spark plug. Inspect the plug before
installing it.
Using spark plugs with an improper heat range
or incorrect reach can cause engine damage.
Before removing the spark plug, clean the spark
plug area thoroughly to prevent dirt from
entering the cylinder.
Ride for 10 - 15 minutes before taking a plug
reading. A new plug will not color immediately.
To obtain an accurate reading of a new spark
plug:
1. Accelerate at full-throttle on a straight.
2. Push the engine stop button and pull the
clutch lever in to release the clutch.
3. Coast to a stop.
4. Remove the spark plug.
5. Use a magnifying glass to inspect the spark
plug. The porcelain insulator (1) around the
center electrode (2) should appear clean and
colorless with a gray ring around the center
electrode where it exits the porcelain.
Metallic specks indicate lean jetting that is
removing metal from the piston. Black sooty
streaks on the porcelain indicate rich jetting.
NOTICE
Condition
Normal
Overheating
(Lean)
Wet
(Rich)
Spark Plug Appearance
Dark brown to light tan
color with dry electrode
Light gray or white color
Wet or sooty
Mixture
correct
lean
rich
Improperly tightened spark plugs can damage the
engine. If a plug is too loose, a piston may be
damaged. If a plug is too tight, the threads may
be damaged.
NOTICE
(1) insulator (3) side electrode
(2) center electrode
Spark Plug Coloring Guidelines
Remember that in addition to improper jetting:
• A lean condition can be caused by air leaks in
the inlet tract or exhaust system, the passage
of too much air because of the use of the
wrong air cleaner, use of a less-restrictive
aftermarket exhaust system, or a hole or holes
(deliberate or unitentional) in the air box.
• A rich condition can be caused by a plugged
or dirty air cleaner, use of a more-restrictive
aftermarket exhaust system, a clogged spark
arrester, or excessive oil on the air cleaner.
Excessive smoking will occur.
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