2003 YAMAHA YZ250F engine

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Page 616 of 662

YAMAHA YZ250F 2003  Owners Manual 7 - 4
TUNSETTING
1Jet needle
2Pilot air jet
3Needle jet
4Main jet
5Pilot jet
6Pilot screw
Main jet adjustment
The richness of the air-fuel mixture at full throt-
tle can be set by changing the main je

Page 618 of 662

YAMAHA YZ250F 2003  Owners Manual 7 - 5
TUNSETTING
Pilot screw adjustment
The richness of the air-fuel mixture with the
throttle fully closed to 1/4 open can be set by
turning the pilot screw 1. Turning in the pilot
screw will make th

Page 620 of 662

YAMAHA YZ250F 2003  Owners Manual 7 - 6
TUNSETTING
Effects of adjusting the pilot jet (reference)
ÅIdle
ıFully open
1/4 1/2 3/4
+5%
–5%
#42
#38#40
Å
ı
Jet needle groove position adjustment
Adjusting the jet needle 1 position aff

Page 624 of 662

YAMAHA YZ250F 2003  Owners Manual 7 - 8
TUN
Leak jet adjustment (accelerator pump
adjustment) 
The leak jet 1 is a setting part that adjusts the
flow of fuel discharged by the accelerator
pump. Since the accelerator pump operates
only

Page 628 of 662

YAMAHA YZ250F 2003  Owners Manual 7 - 10
TUN
Examples of carburetor setting depending on symptom
This should be taken simply for an example. It is necessary to set the carburetor while checking
the operating conditions of the engine.

Page 632 of 662

YAMAHA YZ250F 2003  Owners Manual 7 - 11
TUN
EC720000
CHASSIS
Selection of the secondary reduction ratio
(Sprocket)
Secondary 
reduction = 
ratio
<Requirement for selection of secondary gear
reduction ratio>
It is generally said that

Page 644 of 662

YAMAHA YZ250F 2003  Owners Manual 7 - 17
TUN
EC72B000
Rear suspension setting
The rear suspension setting should be made
depending on the rider’s feeling of an actual
run and the circuit conditions.
The rear suspension setting inclu
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