Yamaha YZ250 Owner's Service Manual page 28

BREAK-IN PROCEDURES
1. Before starting the engine, fill the fuel tank
with a break-in oil-fuel mixture as follows.
Mixing oil:
YAMALUBE "2-R"
Mixing ratio:
15:1
2. Perform the pre-operation checks on the
machine.
3. Start and warm up the engine. Check the
idle speed, and check the operation of the
controls and the "ENGINE STOP" button.
4. Operate the machine in the lower gears at
moderate throttle openings for five to eight
minutes. Stop and check the spark plug con-
dition; it will show a rich condition during
break-in.
5. Allow the engine to cool. Restart the engine
and operate the machine as in the step
above for five minutes. Then, very briefly
shift to the higher gears and check full-throt-
tle response. Stop and check the spark plug.
6. After again allowing the engine to cool, re-
start and run the machine for five more min-
utes. Full throttle and the higher gears may
be used, but sustained full-throttle operation
should be avoided. Check the spark plug
condition.
7. Allow the engine to cool, remove the top
end, and inspect the piston and cylinder. Re-
move any high spots on the piston with #600
grit wet sandpaper. Clean all components
and carefully reassemble the top end.
8. Drain the break-in oil-fuel mixture from the
fuel tank and refill with the specified mix.
9. Restart the engine and check the operation
of the machine throughout its entire operat-
ing range. Stop and check the spark plug
condition. Restart the machine and operate
it for about 10 to 15 more minutes. The ma-
chine will now be ready to race.
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STARTING AND BREAK-IN
• After the break-in or before each race, you
must check the entire machine for loose
fittings and fasteners as per "TORQUE-
CHECK POINTS". Tighten all such fasten-
ers as required.
• When any of the following parts have been
replaced, they must be broken in.
CYLINDER AND CRANKSHAFT:
About one hour of break-in operation is
necessary.
PISTON, RING AND GEARS:
These parts require about 30 minutes of
break-in operation at half-throttle or less.
Observe the condition of the engine care-
fully during operation.
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