Leak Jet Adjustment (Accelerator Pump Adjustment); Relationship With Throttle Opening - Yamaha YZ250F(V) Owner's Service Manual

1
SETTING
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> #80 → #70
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> #80 → #90
Standard leak jet
* Except for USA and CDN

Relationship with throttle opening

The flow of the fuel through the carburetor
main system is controlled by the main jet and
then, it is further regulated by the area
between the main nozzle and the jet needle.
The fuel flow relates to the diameter of the
straight portion of the jet needle with the throt-
tle 1/8 to 1/4 open and relates to the clip posi-
tion with the throttle 1/8 to 3/4 open.
Therefore, the fuel flow is balanced at each
stage of throttle opening by the combination of
the jet needle straight portion diameter and clip
position.
7 - 8
T U N
#80
* #85