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122 Adjustments for Competition
21. Tighten the insulator band screw (17) so the
gap between the tabs of the clamp is 0.3 ±
0.04 in (7 ± 1 mm).
(17) insulator band screw
22. Start the engine.
If the engine idle speed is too high or too
low or engine is not idling, adjust the engine
idle speed (page 48).
23. Repeat steps 4 – 22 until the engine gives
maximum power with the correct spark plug
reading. It is always better to jet a little rich
than a little lean. It is advisable to record the
settings, course conditions, lap times, and
climatic and barometric conditions for future
reference.
(17)
0.3 ± 0.04 in
(7 ± 1 mm)
Carburetor Adjustments & Tuning Tips
Spark Plug Reading
Refer to Spark Plug on page 52.
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
An improperly tightened spark plug can damage
the engine. If a plug is too loose, a piston may
be damaged. If a plug is too tight, the thr eads
may be damaged.
NOTICE
(1) porcelain 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 unintentional) in the air cleaner
housing.
• 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.
(2)
(3)
(1)
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