O.S. Engines 91HZ-R - Manual (Page 15)

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In case the engine does not stop.
Hold the rotor head, and pinch the fuel line to stop the
fuel supply. If it still does not stop, pull off the fuel line
from the carburetor.
It is necessary to readjust the throttle linkage so that
the carburetor rotor is fully closed when the throttle
stick and throttle trim on the transmitter are fully
pulled Down.
NOTE:
If the throttle response is poor or the engine
stops due to a temporarily over-rich mixture im-
mediately after the engine is started, pinch the
fuel line for one or two seconds until the engine
r.p.m. increase and the engine runs steadily.
Reminder!
Never touch, or allow any object to
come into contact with, the rotating
rotor.
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All internal-combustion engines benefit, to some
degree, from extra care when they are run for the first
few times known as running-in or breaking-in.
This allows the working parts to mate together under
load at operating temperature.
However, because O.S. engines are made with the
aid of the finest modern precision machinely and from
the best and most suitable materrials, only a very
short and simple running-in procedure is required and
can be carried out with the engine installed in the
model.
RUNNING-IN ("Breaking-in")
Main needle is set two and half turns open from fully
closed position and the medium speed needle is set
one turn open from fully closed position when the
engine leaves the factory.
It is expected with these needle settings the engine
may run rich. During running-in, hover the model
making sure the engine runs rich.
Also, during running-in since the mixture is rich, you
may feel uneven engine rpm and more fuel
consumption.
In the next section, needle adjustments to optimum
position from running-in position are explained.
Be sure to run the engine a little on the rich side so
that if will have a long life expectancy.