Yamaha yz250f 2012, Owner'S Service Manual

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7-5
ENGINE
This should be taken simply for an example. It is necessary to set the carburetor while checking the operating conditions
of the engine.
Closed to 1/4 throttle
Hard breathing
Speed down
Use jet needle with a smaller diameter. Slow-speed-circuit passage
Clogged → Clean.
Overflow from carburetor
Closed to 1/4 throttle
Poor acceleration
Use jet needle with a larger diameter.
Raise jet needle clip position. (1 groove up)
Poor response in the low to in-
termediate speeds Raise jet needle clip position.
If this has no effect, lower the jet needle clip
position.
Poor response when throttle is
opened quickly Check overall settings.
Use main jet with a lower calibration no.
Raise jet needle clip position. (1 groove up)
If these have no effect, use a main jet with
a higher calibration no. and lower the jet
needle clip position. Check air filter for fouling.
Check that the accelerator pump operates
smoothly.
Symptom Setting Checking