Yamaha YZ250 2021, Owner'S Manual

Page: 132 / 148

ENGINE
8-3
EAM30596
PILOT JET ADJUSTMENT
The richness of air-fuel mixture with the throttle
fully closed to 1/2 open can be set by turning the
pilot jet “1”. It is changed when adjustment can-
not be made by the pilot air screw alone.
A larger size jet results in a richer mixture at low
speeds, and a smaller size in a leaner mixture.
EAM30597
JET NEEDLE ADJUSTMENT
On the carburetors used in the YZ250/YZ250X,
the main nozzle is press-fitted, so it can not be
replaced. Therefore, carburetor setting requires
the change of the jet needle.
1. The jet needle setting parts, having the same
taper angle, are available in different straight
portion diameters and in different taper start-
ing positions.
2. Effects of changing the jet needle (reference)
• Diameter of straight portion
Changing the diameter of the straight portion
adjusts the air-fuel mixture when the throttle
is 1/8 to 1/4 open.
• Taper starting position
Changing the taper starting position produc-
es the same effect as changing the clip posi-
tion by 0.5 groove.
Example:
In case of being 0.5 groove leaner in relation
to N3EW-3rd groove, choose N3CW-3rd
groove.
Standard pilot jet #50
Standard jet needle N3EW
A. Difference in straight portion diameter
B. Difference in taper starting position
a. Diameter of the straight portion
b. Taper starting position
c. Rich
d. Lean
N 3 EG
N 3 EH
N 3 EW
N 8 RW
N 3 EW
N 3 CW
N 8 9W
N 3 EJ
N 3 EK