Yamaha WR250F Owner's Service Manual

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Contents

3-14ENGINEADJUSTING THE ENGINE IDLINGSPEED1. Start the engine and thoroughlywarm it up.2. Adjust:• Engine idling speedAdjustment steps:a. Turn the throttle stop screw "1"until the specified engine idlingspeed.Using a digital engine tachometer foridle speed adjustment, detect the en-gine idling speed by bringing thesensing element "c" of the engine ta-chometer close to the ignition coil "2".ADJUSTING THE VALVECLEARANCE• The valve clearance should be ad-justed when the engine is cool tothe touch.• The piston must be at Top DeadCenter (T.D.C.) on compressionstroke to check or adjust the valveclearance.1. Remove:• Seat• Fuel tankRefer to "SEAT, FUEL TANKAND SIDE COVERS" section.2. Drain:• CoolantRefer to "CHANGING THECOOLANT" section.3. Remove:• Right radiatorRefer to "RADIATOR" section inthe CHAPTER 5.• CarburetorRefer to "CARBURETOR" sectionin the CHAPTER 5.• Spark plug• Upper engine bracket• Cylinder head coverRefer to "CAMSHAFTS" sectionin the CHAPTER 5.4. Remove:• Timing mark accessing screw "1"• Crankshaft end accessing screw"2"• O-ring5. Check:• Valve clearanceOut of specification → Adjust.Checking steps:a. Turn the crankshaft counterclock-wise with a wrench.b. Align the T.D.C. mark "a" on therotor with the align mark "b" on thecrankcase cover when piston is atT.D.C. on compression stroke.In order to be sure that the piston is atTop Dead Center, the punch mark "c"on the exhaust camshaft and thepunch mark "d" on the intake cam-shaft must align with the cylinderhead surface, as shown in the illustra-tion.c. Measure the valve clearance "e"using a feeler gauge "1".Record the measured reading if theclearance is incorrect.6. Adjust:• Valve clearanceAdjustment steps:a. Remove the camshaft (intake andexhaust).Refer to "CAMSHAFTS" sectionin the CHAPTER 5.b. Remove the valve lifters "1" andthe pads "2".To increase idle speed→Turn thethrottle stop screw "1" in "a".To decrease idle speed → Turnthe throttle stop screw "1" out"b".Engine idling speed:1,750–1,950 r/minValve clearance (cold):Intake valve:0.10–0.15 mm(0.0039–0.0059 in)Exhaust valve:0.17–0.22 mm(0.0067–0.0087 in)