O.S. engine FS-70S User Manual

However, as O.S. engines are made with the aid of the finest
modern precision machinery and from the best and most
suitable materials, only a very short and simple running-in
procedure Is required and can be carried out with the
engine installed in the model.
For running-in, use the same sized propeller as you intend
for flying your model.
Running-in procedure is as follows:
Start the engine and run it for about 5 seconds at around
maximum r.p.m., then open the needle-valve %2 turn to
produce a rich mixture for cooler, slower running, and run
for 20 seconds at this setting. Keep the throttle fully open,
using only the needle-valve to reduce speed. Repeat this
procedure, alternately running the engine fast and slow
with the needle-valve, but gradually extending the short
periods of maximum speed running until two full tanks of
fuel are consumed.
Note: Take care to avoid dusty and sandy locations. Dust and grit
drawn into the engine will seriously damage its working parts.
Following the initial running-in on the ground, the engine
should be given a period of moderately rich running in the
air. For the first flights, set the needle-valve rich, consistent
with adequate take-off power and steady level flight and, if
necessary, readjust the throttle trim on the transmitter so
that the engine does not stop when the throttle is fully
closed.
With each successive flight, close the needle-valve slightly,
until, at the end of 10 flights, the needle-valve is set for
maximum power. The carburettor can now be adjusted for
optimum throttle performance following the instructions
given tn the next section.
Note: Remember that, while the engine is being run-in and the
needle-valve is set on the rich side, the carburettor cannot be
expected to show its best response. Therefore, avoid abrupt
throttle operation at this stage.
ADJUSTING THE CARBURETTOR
The carburettor of your FS-70S has been factory set for the
approximate best result, but the settings may, in some
cases, vary slightly in accordance with fuel and climatic
conditions.
If the desired throttle response is not obtained after the
completion of the running-in period, the carburettor should
be re-adjusted as follows. Please refer to Photos 2 and 3.
Three adjustable controls are provided on this carburettor.
© The Needle-Valve: For adjusting the mixture strength
when the throttle is fully open.
è The Mixture Control Screw: For adjusting the mixture
strength at part-throttle and idling speeds, to obtain
steady idling and smooth acceleration to medium speeds.
@ The Throttle Stop Screw: For establishing the minimum
idling speed. (see Photo 3)
Mixture control screw
Needie valve
Photo 2
1. Set the throttle lever 1/4 open from the fully closed
position (see Fig. 3) and start the engine in the usual
way. It is preferable to have the throttle only slightly
open, to avoid unnecessarily high revolutions when the
engine starts.
2. Now open the throttle fully and gradually close the
needle-valve until the engine is running at its optimum
rp.m. in the air. The needle-valve setting at this time
will be 1/8 to 1/4 open from the maximum r.p.m.
setting.
Note: Make sure that the engine ts fully “run-in” before operating it
continuously at full power. {See RUNNING IN section.)
3. Having set the needle-valve as described above, close the
throttle and run the engine at idling speed for approxi-
mately 5 seconds, then steadily move the throttle to the
fully open position by means of the throttle servo.
(a) If, at this point, the engine hesitates before picking
up speed, with a low-pitched exhaust note and an
excess of exhaust smoke, it is probable that the idling
mixture is too rich. In this case, it will be necessary
to turn the mixture control screw clockwise about 45
degrees.
(b} If, on the other hand, the engine hesitates or even
appears to cease firing for an instant, before in-
creasing speed, it is probable that the idling mixture ts
too lean. In this case, it will be necessary to turn the
mixture control screw counter-clockwise about 90
degrees then turn it clockwise 45 degrees.
Turn the mixture control screw 30 to 45 degrees at a time
in the early stages. When the response improves, turn the
mixture control screw 10 to 15 degrees at atime. Carry
out adjustments progressively and patiently remembering
the symptoms of rich and lean running, quoted above, until
the engine responds quickly and positively to the throttle.
4. The throttle stop screw is for fixing the minimum idling
speed. If, after carrying out mixture adjustments, the
idling speed is found to be too high, the throttle stop
screw should be turned counter-clockwise until the
desired idling speed is obtained.
Note: Once the correct carburettor settings have been established, it
should be unnecessary to alter them. Such slight needle-valve
readjustments as may be required to compensate for varia-
tions in atmospheric conditions, will not normally affect the
other two controls. Slight readjustments may be necessary
for optimum performance if different types of fuel, glow-
plugs or propellers are used. In this case, begin by flying the
model with the needle-valve approximately 1/8 to 1/4 turn
open from the peak r.p.m. as a safety measure, then readjust
as necessary. |
REALIGNMENT OF MIXTURE CONTROL VALVE
In the course of making carburettor adjustments, it is just
possible that the Mixture Control Valve may be tnadver-
tently screwed in or out too far and thereby moved beyond
its effective adjustment range. Please refer to Fig. 4.
Its basic setting can be reestablished as follows:
First screw in the Mixture Control Valve, while looking into
the rotor hole. (See small sketch.) Then, gradually unscrew
the Mixture Control Valve
until ‘A’ is precisely tangential
to the rotor hole (i.e. so that
‘A’ and ‘B’ are superimposed).
Finaily, unscrew the Mixture
Control Valve a further 180°,
as in the main sketch. This is
the basic (factory) setting for
the Mixture Control Valve.
Mixture control
valve
Throttle
rotor hole
CARBURETTOR CLEANLINESS
The correct functioning of
the carburettor depends on
its small fuel orifices remain-
ing clear. The minute particles
of foreign matter that are pre-
sent in any fuel can easily
partially obstruct these
orifices and upset mixture
strength so that engine per-
formance 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 carburettor and, furthermore,
that this filter is frequently cleaned to remove dirt and lint
that accumulates on the filter screen. Finally, ocasionally
Throttle
stop screw
Dirt and fibrous
matter mostly
accumulate here. x
Photo 3

O.S. engine FS-70S Specifications

General

Brand	O.S. engine
Model	FS-70S
Category	Engine
Language	English