Yamaha WR250F Manuel D'atelier page 640

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7 - 4
SETTING
1 Jet needle
2 Main air jet
3 Pilot air jet
4 Needle jet
5 Main jet
6 Pilot jet
7 Pilot screw
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)
Å
1/4 1/2
#180
#160
Å Idle
ı Fully open
T U N
#170
ı
3/4
+10%
#170
–10%