Horizon Hobby LOSR1900 Manuel D'instructions page 23

Follow this procedure for a proper break-in:
Start the engine and let it run at idle for a complete
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fuel tank. The idling must be stable: if the RPM rise,
open the idle screw of 1/4 turn; if the RPM
decrease, close the idle screw 1/4 turn.
After the first tank, let the engine cool down,
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making sure the piston is not in the top dead center
position.
Move to a track, the goal is to operate the engine in
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realistic conditions, where the engine cooling is
made by the air flowing over the head. Avoid the
engine reaching high RPM. The engine sound should
be of a low pitch, similar to that of a four-stroke
engine. Smoke and unburned fuel should exit from
the pipe. If the RPM rise too high at 80% throttle,
immediately slow down and open the top end needle
in 1/4 turn increments until lower RPM are achieved.
Continue running this way for 0.5L (500cc) of fuel,
but avoid running at full throttle for a long time.
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Once you have run 0.5L (500cc) through the engine,
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you can close the top end screw to achieve up to
80% of normal engine performance, and run the
engine for 0.25L (250cc) fuel with higher RPM.
Always make sure you see plenty of white smoke
coming from the exhaust during this time.
In the last phase (carburetion optimization) you can
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reach 90% of normal performance. Avoid engine
overheating, which implies power loss. In this case,
slow down immediately and open the top end screw
of 1/4 turn.
During the break-in procedure the engine
should maintain a regular idling and plenty
of smoke should come from the exhaust
pipe.
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