RUNNING-IN ("Breaking-in")
ADJUSTMENT
CARE AND MAINTENANCE
Please pay attention to the matters described
below to ensure that your engine serves you well
in regard to performance, reliability and long life.
As previously mentioned, it is vitally important to
avoid operating the engine in conditions where dust,
disturbed by the propeller, may be deposited on the
engine and enter its working parts.
Remember to keep your fuel container closed to
prevent foreign matter from contaminating the fuel.
Install a fuel filter to prevent foreign matter in the fuel
container from entering the fuel tank. O.S. Super
Filters (L) and (S) are available as optional extras.
Install an in-line fuel filter between the tank and
carburetor to prevent foreign matter in the tank from
entering the carburetor.
If these precautions are neglected, restriction of fuel
flow may cause the engine to cut out, or the fuel/air
mixture to become too lean causing the engine to
overheat.
Clean these filters periodically.
The use of modern high-performance alcohol based
model engine fuels, while promoting cooler running,
improved anti-detonation combustion and increased
power, have the disadvantage of causing corrosion
due to the acid by-products of combustion.
The use of nitromethane in the fuel can also
contribute to the problem.
Do not close the needle-valve and mixture control
valve too far as this will cause a lean setting and
over heating of the engine. This can, in turn, create
nitromethane oxide leading to internal rusting of the
engine. Always adjust the needlevalve slightly on the
rich side of peak rpm.
Do not leave unused fuel in the engine at the
conclusion of a day’s flying. Accepted practice is to
cut off the fuel supply while the engine is still running
at full throttle, then expel as much fuel residue as
possible by turning the engine over 5-10 seconds
with the electric starter.
Finally, inject some after-run oil through the glowplug
hole and turn the engine over several times by hand.
Stopping the engine
Fully pull down the throttle trim on the transmitter.
Starting
Preparation of starting
7.
8.
9.
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 immediately
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.
Please observe the following before beginning to
make any adjustment.
Medium-Speed Needle Valve.
Turn approximately 30 degrees (3 to 4 clicks) at a time.
ADJUSTMENT PROCEDURE
This condition may also be initiated by an excessively
prolonged warming-up period. lf, on the other hand,
the mixture is too Iean, this wiIl be indicated by a
marked lack of exhaust smoke and a tendency for the
engine to cut out when the throttle is opened. ln this
case, turn the Mixture Control Screw counter-clockwise
5 degrees to enrich the mixture.
Throttle Opening
Fully Closed
1/3
2/3
Fully Open
Fuel Flow
Maximum
Minimum
Adjustment range of Idle Mixture
Control Screw
Adjustment range of Medium
Speed Needle Valve
Needle Valve too
far open
Needle Valve too
far closed
High Speed Needle
Valve Setting varies
according to the curve.
SUBSEQUENT READJUSTMENTS
CARBURETOR CLEANLINESS
Remove this with
an 8mm wrench
Dirt and foreign matter
mostly accumulate here
6. Priming
5. Inserting the starter shaft
Insert the starting shaft into the shaft
cup securely.
Without energizing the glowplug,
open the throttle a little from the idle
position. Turn the engine over using
the starter until the fuel is seen to
reach the carburetor.
Connect the battery to the glowplug and start the
engine by applying the starter. When started, switch
off the starter and withdraw the starting shaft after
making sure the rotation of the starter shaft stops.
Hold the rotor head by hand so that
rotor cannot rotate when the engine
is Started. Also, steady the model
with a foot on the landing gear skid.
Make sure that the transmitter
throttle stick is at the fully closed
position and the throttle trim at center
position, and make sure that idle-up
switch on the transmitter is off.
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.
For the first few flights with a new engine i.e. while the
engine is being run-in set the needle-valve for a
slightly rich mixture not excessively rich as this may
result in poor throttle response and cause the engine
to stop.
About one half turn open from the nomal setting will
usually suffice.
High-Speed Needle Valve.
Turn this approximately 30 degrees (3 to 4 clicks) at
a time, when making initial adjustments; then in
steps of approximately 15 degrees (1 to 2 clicks)
when making final adjustments.
Idle Mixture Control Screw.
Turn approximately 5 degrees at a time. It turns
approximately 90 degrees both sides from the
center. Turn left to enrich the idle mixture and turn
right to lean the idle mixture.
The general course of adjustment procedure is
shown in the ADJUSTING CHART and is correct
for a fuel containing 20% lubricant and 15-30%
nitromethane.
Bear in mind that fuels containing relatively large
percentages of power-boosting nitromethane operate
at richer mixture settings than are needed for mild
fuels and will, therefore, require the High-Speed
Needle Valve to be readjusted accordingly. The type
and percentage of lubricant used is also a factor here,
as noted later in these instructions.
This carburetor is not equipped with a throttle stop
screw. Instead, idle speed is adjusted by means of
the throttle trim lever on the transmitter.
As a safety measure, first check the transmitter
controls, including the throttle stick and trim lever
positions, and hold the main rotor securely before
starting the engine.
Warm the engine by allowing it to idle for about 30
seconds. If the engine stops, advance the throttle
trim lever slightly to increase the idle rpm.
Then open the throttle sufficiently to 'float' the model
above the ground. lf, at this time, the engine is slow
to pick up and produces an excess of exhaust
smoke, the mixture is too rich.
Correct this condition by turning the Mixture Control
Screw clockwise 5 degrees. lf the mixture is extremely
rich, engine rpm will become unstable: opening the
throttle will produce a great deal of smoke and rpm
may drop suddenly or the engine may stop.
1.
Having provisionally set the idle mixture, the next step
is to adjust the mixture for hovering flight.
Hover the model and actuate the throttle to observe
response over the medium speed range. lf the engine
smokes excessiveIy and throttle response is poor, the
mixture is too rich ; in which case, land the model and
turn the High-Speed Needle Valve clockwise. Do not
close the High-Speed NeedIe Valve more than the
recommended initial adjustment (3 to 4 clicks) at a
time, keeping it a little on the rich side at this stage. DO
NOT touch the Medium Speed Needle Valve.
lf, on the other hand, hovering is not stable and response
to the throttIe is over-sensitive, or if the engine tends to
overheat, this indicates that the mixture is too lean and
should be corrected by turning the High-Speed Needle
Valve counter-clockwise.
2.
When satisfactory hovering flight has been achieved, land
the modeI again and re-check the engine's idle qualities.
After about 10 seconds of idling, open the throttle to
'float' the model. lf the transition is smooth, the idle
mixture is O.K. If the symptoms of either rich or Iean
running are observed, readjust the Idle Mixture Control
Screw accordingly.
NOTE: With this carburetor, neither the Idle Mixture
Control Screw adjustment, nor the Medium Speed
Needle Valve adjustment will have any effect on
mixture strength when the throttle is fully (or
almost fully) open.
Now adjust the High-Speed Needle Valve to achieve
the best performance when the model is flying at full
throttle. lf, at full throttle, acceleration is poor, the exhaust
unduly smoky and the model fails to reach expected
straight line speed, the mixture is too rich and the
High-Speed Needle Valve setting will need to be
reduced.
lf, however, after smoothly acceIerating to satisfactory
high-speed straight and level flight, power is lost
when the model is puIled up into a climb, the mixture
is too lean. ln this case, land the model immediately
and readjust the High-Speed Needle Valve to a richer
setting.
3.
4. Having now found the optimum setting for the High-Speed
Needle Valve, re-check the engine's idle performance,
fine tuning the Idle Mixture Control Screw, if necessary, to
perfect the idle.
Now re-check hovering performance It may be found
that (with the High-Speed Needle Valve now set for
optimum full-throttle performance) hovering will
reveal symptoms of slightly lean running at medium
speeds. DO NOT touch the High-Speed Needle Valve.
5.
It is at this point that the Medium Speed Needle
Valve, previously set two turns open, may be
brought into operation. Open the Medium Speed
Needle Valve 30 degrees, or 3-4 clicks, then fine
tune until the optimum hovering performance is
obtained.
If on the other hand, hovering reveals rich running,
close the Medium Speed Needle Valve gradually
until the optimum hovering performance is obtained.
Once the engine has been run-in and the carburetor
controls properly set up, it should be unnecessary to alter
the mixture settings, except to make minor changes to the
Main (High-Speed) Needle Valve occasionally, to take
account of differences in climatic condisitions. However,
as previously mentioned, the use of a different fuel,
particularly one containing more, or less, nitromethane
and / or a different type or proportion of lubricating oil, is
likely to call for some modification to the High-Speed
Needle-Valve adjustment. As a safety measure, it is
advisable to increase the High-Speed Needle Valve
setting by an extra half-turn counter-clockwise, prior to
establishing the new setting. The same applies if the
silencer type is changed. A different silencer may alter the
exhaust pressure applied to the fuel feed and call for a
revised Needle-Valve setting. The use of a different
glowplug, or changes to the main rotor and its pitch
angles may also require compensating carburetor
readjustments.
The correct functioning of the carburetor depends on
its small fuel orifices remaining clear. The minute
particles of foreign matter that are present in any fuel
can easily partially obstruct these orifices and upset
mixture strength so that engine performance becomes
erratic and unreliable. It is recommended that fuel is
passed through a filter when the tank is filled and that
a good in-line filter is installed between the fuel tank
and carburetor and, furthermore, that this filter is
frequently cleaned to remove foreign matter that
accumulates on the filter screen. Finally, occasionally
remove the needle-valve holder from the carburetor as
shown in Photo and extract any remaining foreign
matter that may have lodged in the location shown in
Photo, below.
