Yamaha WR450F Manuel D'atelier Du Proprietaire page 720

1
SETTING
Effects of changing the jet needle (refer-
ence)
(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
1/4
È Idle
É Fully open
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 when throttle is open, the leak jet is used
to adjust a fuel mixture ratio for quick throttle
opening and is therefore different from other
setting parts that adjust a fuel mixture for each
throttle opening (each engine speed).
1. The engine breathes hard in quick throttle
opening.
Select a leak jet having lower calibrating
No. than standard to enrich the mixture.
<Example> #50 → #45
2. Rough engine operation is felt in quick
throttle opening.
Select a leak jet having higher calibrating
No. than standard to lean out the mixture.
<Example> #50 → #55
Standard leak jet
7 - 6
T U N
1/2 3/4
R
T
#50
É
+10%
S
–10%