Yamaha WR250FM service manual Leak jet adjustment accelerator pump adjustment

SETTING

T U N

1

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> #90 → #80

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> #90 → #100

Standard leak jet

#90

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.

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