Yamaha WR250FM service manual Setting T U N

1

SETTING T U N

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.

Standard pilot	2 (example)
screw position	* 1-7/8

* Except for USA

NOTE:

•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)

È 1/4 1/2 3/4 É

+5%

1

3

2

–5%

ÈIdle

ÉFully open

1 2-1/2 turns out

2 1-1/2 turns out

3 2 turns out

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 #40

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