10
MIXTURE CONTROLS
The Needle Valve
When set to produce maximum power at full throttle, this
establishes the basic fuel/air mixture strength. The correct
mixture is then maintained by the carburetor's built-in
automatic mixture control system to cover the engine's
requirements at reduced throttle settings.
Two mixture controls are provided on these engines.
•
The Mixture Control Valve (carburetor)
This meters fuel flow at part-throttle and idling speeds to
ensure reliable operation as the throttle is opened and
closed. The Mixture Control Valve is factory set for the
approximate best result. First run the engine as received
and readjust the Mixture Control Screw only if necessary.
•
STARTING
Fill the fuel tank. Do not allow fuel to overflow into the
silencer, otherwise the engine may become flooded and
difficult to start.
Check that the needle-valve is closed. (Do not overtighten.)
Now open the needle-valve 1-1.5 turns (when the standard
E-5010 silencer is used) or 1.5-2 turns (when a tuned
silencer is used), from the fully closed position.
Turn needle-valve clockwise to close
(for leaner mixture)
Turn needle-valve counter-clockwise to
open (for richer mixture)
Mark
Close
Open
1.
2.
5.
Connect battery leads to glowplug.
(This is to avoid unnecessarily high
r.p.m. when the engine starts.)
Bring electric starter into contact with spinner and depress
starter switch for one or two seconds. Repeat if necessary.
When the engine starts, withdraw the starter immediately.
7.
Attention :
Do not choke the carburetor air intake when applying the
starter. This could cause an excessive amount of fuel to be
drawn into the cylinder which may initiate an hydraulic lock
and damage the engine.
If the engine does not start within 10 repeat applications of
the starter, remove the glow-plug, check that it glows brightly
and that the cylinder is not flooded with fuel. (To eject excess
fuel, close needle-valve and apply starter with glowplug
removed.) Then try again.
8. When the engine starts, advance the throttle stick slowly
checking the increase of r.p.m. Abrupt throttle operation
right after starting may cause the engine to stumble or stop.
VERY IMPORTANT!
Before being operated at full power (i.e. at full-throttle and with the
needle-valve closed to its optimum setting) the engine must be
adequately run-in, otherwise there is a danger of it becoming
overheated and damaged. (See RUNNING-IN ["Breaking-in"] .)
6.
Set the throttle rotor slightly open
(2-3mm) from the closed position.
2-3mm
11
RUNNING-IN ("Breaking-in")
All internal-combustion engines benefit from extra care when
they are run for the first few times - known as running-in or
breaking-in. This is because the working parts of a new engine
take some time to settle down after being subjected to high
temperatures and stresses. Therefore, it is vitally important to
complete the break-in before allowing the engine to run
continuously at high speed and before finalizing carburettor
adjustments. However, because O.S. engines are produced
with the aid of the finest modern precision machinery and
from the best and most suitable materials, only a short and
simple running-in procedure is called for and can be carried
out with the engine installed in the model.
The process is as follows.
Install the proper propeller intended for your model. Open
the needle-valve and start the engine. Run the engine for
two to three minutes with the throttle fully open, but with the
needle-valve adjusted for rich, slow "four-cycle"operation.
Now close the needle-valve until the engine speeds up to
"two-cycle"operation and allow it to run for about 10
seconds, then reopen the needle-valve to bring the engine
back to "four-cycle"operation and run it for another 10
seconds. Repeat this procedure until the fuel tank is empty.
Refer to IDLING ADJUSTMENT section and fix the idling
position where the lowest possible r.p.m., with steady
running, is obtained.
Re-start and adjust the needle-valve so that the engine just
breaks into "two-cycle" from "four-cycle" operation, then
make three or four flights, avoiding successive "nose-up"
flights.
1.
2.
3.
4.
During subsequent flights, the needle-valve can be
gradually closed to give more power.
However, if the engine shows signs of running too lean, the
next flight should be set richer. After a total of ten to fifteen
flights, the engine should run continuously, at its optimum
needle-valve setting, without loss of power.
Optimum Needle setting (1)
Slowly advance the throttle to its fully open position, then
gradually close the needle-valve until the exhaust note
begins to change.
At this point, disconnect the battery from the glowplug,
taking care that the battery leads or glowplug clip do not
come into contact with the rotating propeller. If the engine
stops when the battery is disconnected, close the needle-
valve about 30˚ and restart.
Optimum Needle setting (2)
As the needle-valve is closed slowly and gradually, the
revolutions of the engine will be increased and a
continuous high-pitched exhaust note, only, will be heard.
Close the needle-valve 10-15˚ and wait for the change of
r.p.m.
After the revolutions of the engine are increased, turn the
needle-valve another 10-15˚ and wait for the next change
of r.p.m. As the speed of the engine does not instantly
change with needle-valve readjustment, small movements,
with pauses between, are necessary to arrive at the
optimum setting.
5.
