Yamaha YZ250T1 Owner's Service Manual page 252

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EC719081
Jet needle adjustment
(For EUROPE)
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
<Example>
N3EW - 3
A Difference in straight portion dia.
B Difference in taper starting position
c Rich
d Lean
2. Effects of changing the jet needle (reference)
9 Diameter of straight portion
Changing the diameter of the straight por-
tion adjusts the air-fuel mixture when the
throttle is 1/8 to 1/4 open.
9 Taper starting position
<Difference of 0.5 groove>
Rich N3EW-4th groove
N3EW
Lean N3EW-2nd groove
Changing the taper starting position pro-
duces the same effect as changing the clip
N3CW
position by 0.5 groove.
<Example>
In case of being 0.5 groove leaner in rela-
tion to N3EW-3rd groove, choose N3CW-
3rd groove.
A In case of being 0.5 groove leaner in relation
to N3EW-3rd groove.
a Difference of 0.5 groove
7-7
TUN
SETTING
Clip position
Diameter a of straight portion
Taper starting position b
0.5
N3CW-4th groove
0.5
N3EW-3rd groove
0.5
N3CW-3rd groove
0.5
N3EW