Yamaha TT-R125 Manuel D'atelier Du Proprietaire page 268

CARBURETOR
HANDLING NOTE
At high altitudes, the atmospheric pressure is
lower. This can make the fuel mixture too rich,
leading to such problems as fouled.
Spark plugs and slow response at high engine
speeds. A special part, High Altitude Main Jet
1 #102.5 (620-1423A-71-A0) is available to
correct this.
EC463000
REMOVAL POINTS
Throttle valve
1. Remove:
Throttle valve 1
G
Spring (throttle valve) 2
G
Carburetor top cover 3
G
Throttle cable 4
G
NOTE:
While compressing the spring (throttle valve),
disconnect the throttle cable.
Pilot air screw
1. Remove:
Pilot air screw 1
G
NOTE:
To optimize the fuel flow at a smaller throttle
opening, each machine's pilot air screw has
been individually set at the factory. Before
removing the pilot air screw, turn it in fully and
count the number of turns. Record this number
as the factory-set number of turns out.
4 - 5
ENG