SETTING

T U N

Jet needle adjustment

The jet needle is adjusted by changing it.

Standard jet needle

OBDUT

*OBDUQ

* Except for USA

The tapered sections of all jet needles have the same starting positions, but the needles are available with different straight-portion diameters.

<Example> OBDUT - 4

Clip position

Diameter a of straight portion

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.

Å

1/4

1/2

3/4

S

U

ÅIdle ı Fully open

ı

+10%

T

–10%

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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Image 325
Yamaha WR45OFR Jet needle adjustment, Standard jet needle, Obdut Obduq, Effects of changing the jet needle reference