Yamaha wr250f Owner's Service Manual

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7 - 10T U NExamples of carburetor setting depending on symptomThis should be taken simply for an example. It is necessary to set the carburetor while checkingthe operating conditions of the engine.Symptom Setting CheckingAt full throttleHard breathingShearing noiseWhitish spark plugLean mixtureIncrease main jet calibration no.(Gradually)Discoloration of spark plug →If tan color, it is in good condition.If cannot be corrected:Clogged float valve seatClogged fuel hoseClogged fuel cockCheck that the accelerator pump oper-ates smoothly.At full throttleSpeed pick-up stopsSlow speed pick-upSlow responseSooty spark plugRich mixtureDecrease main jet calibration no.(Gradually)Discoloration of spark plug →If tan color, it is in good condition.If cannot be corrected:Clogged air filterFuel overflow from carburetorLean mixture Lower jet needle clip position.(1 groove down)The clip position is the jet needlegroove on which the clip is installed.The positions are numbered from thetop.Check that the accelerator pump oper-ates smoothly. (except for rich mixturesymptom).Rich mixture Raise jet needle clip position.(1 groove up)1/4 ~ 3/4 throttleHard breathingLack of speedLower jet needle clip position.(1 groove down)1/4 ~ 1/2 throttleSlow speed pick-upPoor accelerationRaise jet needle clip position.(1 groove up)Closed to 1/4 throttleHard breathingSpeed downUse jet needle with a smaller diameter. Slow-speed-circuit passageClogged → Clean.Overflow from carburetorClosed to 1/4 throttlePoor accelerationUse jet needle with a larger diameter.Raise jet needle clip position. (1 grooveup)Poor response in the low tointermediate speedsRaise jet needle clip position.If this has no effect, lower the jet needleclip position.Poor response when throttleis opened quicklyCheck 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 jetwith a higher calibration no. and lowerthe jet needle clip position.Check air filter for fouling.Check that the accelerator pump oper-ates smoothly.Jet needleClipGroobe 7Groobe 6Groobe 5Groobe 4Groobe 3Groobe 2Groobe 1Leaner↑(Standard)↓Richer*SETTING

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