Yamaha 20D Owner's Manual page 100

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Make sure to mix gasoline (petrol) and oil
completely, otherwise your outboard
motor may be damaged.
EMU01786
Break-in procedure
Run the engine under load (in gear with a
propeller installed) as follows.
1) First 10 minutes:
Run the engine at the lowest possible
speed. A fast idle in neutral is best.
2) Next 50 minutes:
Do not exceed half throttle (approxi-
mately 3,000 r/min). Vary engine
speed occasionally. If you have an
easy-planing boat, accelerate at full
throttle onto plane, then immediately
reduce the throttle to 3,000 r/min or
less.
3) Second hour:
Accelerate at full throttle onto plane,
then reduce engine speed to three-
quarter throttle (approximately 4,000
r/min). Vary engine speed occasional-
ly. Run at full throttle for one minute,
then allow about 10 minutes of opera-
tion at three-quarter throttle or less to
let the engine cool.
4) Third through tenth hours:
Avoid operating at full throttle for
more than 5 minutes at a time. Let the
engine cool between full-throttle runs.
Vary engine speed occasionally.
For premix models
5) After the first 10 hours:
Operate the engine normally. Use the
standard premix ratio of gasoline and
oil. For details on mixing fuel and oil,
see "Gasoline and oil mixing" in this
chapter.
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GB