TUNING 155
j
Test Runs
•
With all carburetor settings on s tandard, warm up
the engine, run two or three laps of the course
and examine the spar
k plug condition with varying
throttle openings.
Fuel/Air Mixture Adjustment
Spark Plug Insulator Condition
Mixture
Dry and a light tan color
Correct
Whitish Too lean
Wet and sooty Too rich
•
If the spark plug insulator is whitish, the fuel/air
mixture is too lean. Increase the main jet size by
one step.
•
If the spark plug insulator is wet, the fuel/air mix-
ture is too rich. Reduce the main jet size by one
step.
•
Tune the carburetor so that the engine delivers
satisfactory power at all throttle openings.
NOTE
○
If the fuel/air mixture is too lean, the engine tends
to overheat and may seize up. On the other hand,
if the fuel/air mixture is too rich, the spark plug
gets wet, which causes misfiring. The richness
of the mixture varies depending on atmospheric
conditions (pressure, humidity, and temperature).
Adjust the carburetor taking these conditions into
consideration.
Altitude and Temperature Correction Factors
NOTE
○
For the following recommendations to be applica-
ble, you must use the standard settings as a base.
Do not change any of the settings until you have
determined which are necessary. All specifica-
tions are based o n t he u se of the specified fuel
and oil.