Yamaha YZ125(S)/LC Owner's Service Manual page 510

SETTING
EC716001
Pilot air screw adjustment
The richness of air-fuel mixture with full closed to
1/4 throttle can be set by turning the pilot air
screw 1.
Turning in the pilot air screw will enrich the mix-
ture at low speeds, and turning out it will lean out
the mixture.
Standard pilot air
screw position
*For EUROPE
EC71R010
Pilot jet adjustment
The richness of air - fuel mixture with the throttle
fully closed to 1/2 open can be set by turning the
pilot jet 1.
It is changed when adjustment cannot be made
by the pilot air screw alone.
Standard pilot jet
*For EUROPE
7-4
TUN
1-3/4 turns out
*2 turns out
#40
*#37.5