Yamaha YZ450F, Owner'S Service Manual

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T U N
Jet needle adjustment
The jet needle is adjusted by changing it.
The jet needle setting parts, having the same
taper angle, are available in different straight
portion diameters and in different taper starting
positions.
<Example>
NFPR - 4
Clip position
Diameter
a
of straight portion
b
Reference needle
c
0.5 leaner
Changing from NFPR-4 to NFLR-4 has the
same effect as a lowering of 0.5 clip position.
Standard jet needle NFPR
c
b
NFPR-4
NFLR-4
Diameter of straight portion
Clip position
Rich Lean
N P Q R S T U
Rich
Lean
1 richer NFPN-5 NFPP-5 NFPQ-5 NFPR-5 NFPS-5 NFPT-5 NFPU-5
0.5 richer NFLN-5 NFLP-5 NFLQ-5 NFLR-5 NFLS-5 NFLT-5 NFLU-5
STD NFPN-4 NFPP-4 NFPQ-4 NFPR-4 NFPS-4 NFPT-4 NFPU-4
0.5 leaner NFLN-4 NFLP-4 NFLQ-4 NFLR-4 NFLS-4 NFLT-4 NFLU-4
1 leaner NFPN-3 NFPP-3 NFPQ-3 NFPR-3 NFPS-3 NFPT-3 NFPU-3
SETTING
Effects of changing the jet needle
(reference)
(Diameter of the straight portion)
Changing the diameter of the straight portion
adjusts the air-fuel mixture when the throttle is
1/8 to 1/4 open.
È
Idle
É
Fully open
1/4 1/2 3/4
+10%
R
–10%
Q
S
È É