Yamaha YZ250N Owner's Service Manual page 534

SETTING
EC71B011
Relationship with throttle opening
The flow of the fuel through the carburetor main
system is controlled by the main jet and then, it is
further regulated by the area between the main
nozzle and the jet needle. On the relationship
between the fuel flow and the throttle opening,
the fuel flow relates to the jet needle straight por-
tion diameter around 1/8 to 1/4 throttle opening,
whereas around 1/4 to 1/1 throttle opening it
relates to the taper starting position and to the
clip position.
Therefore, the fuel flow is balanced at each stage
of throttle opening by the combination of the jet
needle straight portion diameter, taper starting
position and clip position.
<Example>
(For USA, CDN, ZA, AUS and NZ)
N3EJ-2nd groove
N3EJ-3rd groove
N3EK-2nd groove
N8RJ-2nd groove
(For EUROPE)
N3CW-3rd groove
N3CW-4th groove
N3CJ-3rd groove
N3EW-3rd groove
å Lean (larger diameter)
∫ Rich (smaller diameter)
1 1/8 throttle
2 1/4 throttle
3 1/2 throttle
4 1/1 throttle
a Main nozzle
7-8
TUN