Yamaha YZ125/LC Manuel D'atelier Du Proprietaire page 506

A
B
C
SETTING
That is:
9 Higher temperature expands the air with its
resultant reduced density.
9 Higher humidity reduces the amount of oxygen
in the air by so much of the water vapor in the
same air.
9 Lower atmospheric pressure (at a high altitude)
reduces the density of the air.
EC713001
Test run
After warming up the engine equipped with the
standard type carburetor(s) and spark plug(s),
run two or three laps of the circuit and check the
smooth operation of the engine and discoloration
of spark plug(s).
Discoloration
Normal
Over burned
(too lean)
Oil fouled
(too rich)
å Normal
∫ Over burned (too lean)
ç Oil fouled (too rich)
7-2
TUN
Condition of spark plug
Insulator is dry and
burnt brown.
Insulator is whitish.
Insulator is sooty and
wet.