Pilot Jet Adjustment; Jet Needle Adjustment - Yamaha YZ250 2022 Owner's Service Manual

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.
Standard pilot jet
EAM30597

JET NEEDLE ADJUSTMENT

On the carburetors used in the YZ250, 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.
Standard jet needle
#50
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
2. Effects of changing the jet needle (reference)
• Diameter of straight portion
N3EW
• Taper starting position
10-3
N3EG
N3EH
N3EW
N3EJ
N3EK
Changing the diameter of the straight portion
adjusts the air-fuel mixture when the throttle
is 1/8 to 1/4 open.
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.
ENGINE
N8RW
N3EW
N3CW
N89W