Spark Plug Reading - Honda CRF150R 2020 Owner's Manual & Competition Handbook

Carburetor Adjustments & Tuning Tips
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).
±
0.3 0.04 in
±
(7 1 mm)
(17)
(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.
122
Adjustments for Competition

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.
NOTICE
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
An improperly tightened spark plug can damage
the engine. If a plug is too loose, the piston may be
damaged. If a plug is too tight, the threads may be
damaged.
(1)
(1) porcelain insulator (3) side electrode
(2) center electrode
Spark Plug Coloring Guidelines
Condition Spark Plug
Appearance
Normal Dark brown to light tan
color with dry
electrode
Overheating Light gray or white
(Lean) color
Wet Wet or sooty
(Rich)
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)
Mixture
correct
lean
rich