Yamaha WR450F(T) Owner's Service Manual page 716

SETTING
Main jet adjustment
The richness of the air-fuel mixture at full throt-
tle can be set by changing the main jet 1.
Standard main jet
If the air-fuel mixture is too rich or too lean, the
engine power will drop, resulting in poor accel-
eration.
Effects of changing the main jet (reference)
È
1/4
È Idle
É Fully open
Pilot jet adjustment
The richness of the air-fuel mixture with the
throttle open 1/4 or less can be set by adjust-
ing the pilot jet 1.
Standard pilot jet
Effects of adjusting the pilot jet (reference)
È
1/4
#48
#42
È Idle
É Fully open
7 - 4
T U N
#165
É
1/2 3/4
#175
#155
#45
1/2 3/4
+10%
#165
–10%
É
+5%
#45
–5%