Yamaha YZ250 2021 User Manual

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
N3EG
N3EH
N3EW
N8RW
N3EW
N3CW
N89W
N3EJ
N3EK

Yamaha YZ250 2021 Specifications

General

Engine Type	249cc liquid-cooled 2-stroke; reed-valve inducted
Bore x Stroke	66.4mm x 72.0mm
Compression Ratio	8.9~10.6:1
Ignition	CDI
Transmission	5-speed; multiplate wet clutch
Final Drive	Chain
Suspension Rear	KYB® single shock; fully adjustable, 12.4-in travel
Brakes Front	Hydraulic disc, 270mm
Tires Front	80/100-21
Tires Rear	110/90-19
Width	32.5 in
Height	50.8 in
Wheelbase	58.5 in
Ground Clearance	14.2 in
Fuel Capacity	2.1 gal
Wet Weight	227 lb
Fuel Delivery	Keihin PWK38S carburetor
Suspension Front	KYB® Speed-Sensitive System inverted fork; fully adjustable, 11.8-in travel
Brakes Rear	Hydraulic disc, 245mm