Yamaha YZ250(W)/W1 Owner's Service Manual page 559

Symptom
0~1/4 throttle
Hard breathing
Speed down
0~1/4 throttle
Poor acceleration
White smoke
Unstable at low speeds
Pinking noise
Poor response at extremely
low speed
Poor response in the
range of low to
intermediate speeds
Poor response when
throttle is opened quickly
Poor engine operation
Setting
Use jet needle having a smaller
diameter.
Use jet needle having a larger
diameter.
Lower jet needle clip position.
(1 groove down)
Turn in pilot air screw.
Reduce pilot jet calibration No.
Turn out pilot air screw.
If not effect, reverse the above
procedures.
Raise jet needle clip position.
If no effect, reverse the above
procedures.
Check overall settings.
Use main jet having lower
calibration No.
Raise jet needle clip position.
(1 groove up)
If no effect, reverse the above
procedures.
Turn in pilot air screw.
7-10
SETTING
Number of turns-back ¡
Correct properly
Overflow from carburetor
Dragging brake
Overflow from carburetor
Check air cleaner for fouling.
Check throttle valve operation.
This should be taken simply for an example.
It is necessary to set the carburetor while
checking the operating conditions of the
engine and discoloration of spark plugs.
Normally, carburetor setting is made by
means of the main jet, needle clip position,
pilot jet and pilot air screw. If the result of set-
ting is still unsatisfactory, it is advisable to
change the sizes of the jet needle.
TUN
Checking