Yamaha WR250F Owner's Service Manual page 67

ADJUSTING THE ENGINE IDLING
SPEED
1. Start the engine and thoroughly
warm it up.
2. Adjust:
• Engine idling speed
Adjustment steps:
a. Turn the throttle stop screw "1"
until the specified engine idling
speed.
Using a digital engine tachometer for
idle speed adjustment, detect the en-
gine idling speed by bringing the
sensing element "c" of the engine ta-
chometer close to the ignition coil "2".
→
To increase idle speed
throttle stop screw "1" in "a".
To decrease idle speed
the throttle stop screw "1" out
"b".
Engine idling speed:
1,750–1,950 r/min
ADJUSTING THE VALVE
CLEARANCE
• The valve clearance should be ad-
justed when the engine is cool to
the touch.
• The piston must be at Top Dead
Center (T.D.C.) on compression
stroke to check or adjust the valve
clearance.
1. Remove:
• Seat
• Fuel tank
Refer to "SEAT, FUEL TANK
AND SIDE COVERS" section.
2. Drain:
• Coolant
Refer to "CHANGING THE
COOLANT" section.
3. Remove:
• Right radiator
Refer to "RADIATOR" section in
the CHAPTER 5.
• Carburetor
Refer to "CARBURETOR" section
in the CHAPTER 5.
• Spark plug
• Upper engine bracket
• Cylinder head cover
Refer to "CAMSHAFTS" section
in the CHAPTER 5.
4. Remove:
• Timing mark accessing screw "1"
• Crankshaft end accessing screw
Turn the
"2"
• O-ring
→
Turn
5. Check:
• Valve clearance
Out of specification
Checking steps:
a. Turn the crankshaft counterclock-
wise with a wrench.
b. Align the T.D.C. mark "a" on the
rotor with the align mark "b" on the
crankcase cover when piston is at
T.D.C. on compression stroke.
→
Adjust.
Valve 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)
3-14
ENGINE
In order to be sure that the piston is at
Top Dead Center, the punch mark "c"
on the exhaust camshaft and the
punch mark "d" on the intake cam-
shaft must align with the cylinder
head surface, as shown in the illustra-
tion.
c. Measure the valve clearance "e"
using a feeler gauge "1".
Record the measured reading if the
clearance is incorrect.
6. Adjust:
• Valve clearance
Adjustment steps:
a. Remove the camshaft (intake and
exhaust).
Refer to "CAMSHAFTS" section
in the CHAPTER 5.
b. Remove the valve lifters "1" and
the pads "2".