Yamaha YZ250(V), Owner'S Service Manual

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7-6
SETTING
TUN
EC719081
Jet needle adjustment
(For USA and CDN)
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.
<Example>
N3EJ - 2
Clip position
Diameter
a
of straight portion
Taper starting position
b
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 N3EJ-3rd groove
N3CJ-3rd groove
N3EJ-2nd groove
N3CJ-2nd groove
Lean N3EJ-1st groove
Changing the taper starting position pro-
duces the same effect as changing the clip
position by 0.5 groove.
<Example>
In case of being 0.5 groove leaner in rela-
tion to N3EJ-2nd groove, choose N3CJ-
2nd groove.
A
In case of being 0.5 groove leaner in relation
to N3EJ-2nd groove.
a
Difference of 0.5 groove
Standard jet needle N3EJ
N3CJ
N3EJ
å
a
1
1
2
2 3
3
4 5
4 5
0.5
0.5
0.5
0.5
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