Yamaha WR250F(T) User Manual download pdf (Page 26)

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TUN

SETTING

Pilot screw adjustment

The richness of the air-fuel mixture with the

throttle fully closed to 1/4 open can be set by

turning the pilot screw

1

. Turning in the pilot

screw will make the mixture lean at low

speeds, and turning it out will enrich it.

N

OTE:

●

If the engine idling speed fluctuates, turn the

pilot screw only 1/2 of a turn in either direc-

tion.

●

To optimize the fuel flow at a smaller throttle

opening, each machine’s pilot screw has

been individually set at the factory. Before

adjusting the pilot screw, turn it in fully and

count the number of turns. Record this num-

ber as the factory-set number of turns out.

Effects of adjusting the pilot screw (reference)

Å

Idle

ı

Fully open

1

2-1/4 turns out

2

1-1/4 turns out

3

1-3/4 turns out

Standard pilot

screw position

1-3/4

(example)

1/4 1/2 3/4

+5%

–5%

A

B

1

2

3

Pilot jet adjustment

The richness of the air-fuel mixture with the

throttle open 1/4 or less can be set by adjust-

ing the pilot jet

1

.

Standard pilot jet #42

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