Yamaha YZ250F(R) Owner's Service Manual page 286

SETTING
Jet needle adjustment
The jet needle is adjusted by changing it.
Standard jet needle
* For EUROPE
The tapered sections of all jet needles have
the same starting positions, but the needles
are available with different straight-portion
diameters.
<Example>
OBELP - 4
Clip position
Diameter a of straight portion
Effects of changing the jet needle (refer-
ence)
(Diameter of the straight portion)
Changing the diameter of the straight portion
adjusts the air-fuel mixture when the throttle is
1/8 to 1/4 open.
Å
1/4
N
Q
Å Idle
ı Fully open
7 - 7
T U N
OBELP
*OBEKP
ı
1/2 3/4
+10 %
–10 %
P