O.S. Engines 9B Carb - 29381010 - Manual

INSTRUCTIONS FOR THE O.S. TYPE 9B CARBURETTOR
The O.S. Type 9B carburettor has been designed to provide a correctly balanced mixture of fuel and air at all throttle settings. It
ensures steady power and a smooth response — even to abrupt operation of the throttle. With the special O.S. mixture control
system featured by this carburettor, adjustment can be made easily and accurately.
INSTALLATION AND LINKAGE
• Make sure, when the engine is installed in the aircraft or boat,
that there is a clearance of at least 15mm between the carburettor
air intake and the firewall or adjacent bulkhead.
• This carburettor is not provided with a screw for setting the
throttle opening at the idling position. Instead, the throttle is
set up as follows:
Connect the throttle lever linkage so that the throttle rotor is (a)
fully open when the transmitter throttle stick is fully advanced
and (b) fully closed when the throttle stick is fully retarded.
Adjustment of the throttle rotor opening at the idling position
can then be made with the throttle trim lever on the transmitter.
ADJUSTING THE CARBURETTOR
1. Advance the throttle trim lever so that the throttle rotor opens
approximately 1 mm from the fully closed position as sketched.
Set the needle-valve 1-1/2 to 2 turns (depending on the size of the
engine and type of fuel) open from the fully closed position, and
start the engine.
Warning: When a watercooled marine engine is started on shore
avoid running it at high r.p.m. without load. either by
keeping the throttle in the idling position, or by opening
the needle-valve to reduce speed. Although the engine is
designed to run at high r.p.m. even when new. such com-
ponents as the cylinder, piston, connecting-rod, etc. will
be seriously damaged if they are allowed to become over-
heated.
2. In the case of a marine installation, put the boat on the water
before opening the throttle and then adjust the Needle-Valve for
the approximate best setting.
In the case of a ducted fan model, adjust the Needle-Valve in the
same way as for a normal propeller driven aircraft.
3. The Mixture Control Screw is for adjusting fuel mixture strength
at part throttle and idling speeds. Having set the needle-valve as
detailed above, close the throttle. The engine should idle conti-
nuously and steadily. (If it stops immediately, first try advancing
the throttle trim lever on the transmitter to raise the idling speed
a little.)
(a) If, however, the engine idles unevenly and hesitates when the
throttle is re-opened, it is probable that the idling mixture is
too rich. Check this by closing the throttle again and re-
opening it after about 10 seconds. If the engine now puffs
out a good deal of smoke and hesitates or even stops, it will
be necessary to close the Mixture Control Screw. Therefore,
turn it a few degrees clockwise. (Turn the Mixture Control
Screw in steps of about 10 degrees only, re-checking the
running qualities each time.)
(b) If, instead of being set too rich, the Mixture Control Screw is
set too lean. the engine will stop when the throttle is closed,
or will lose speed while idling and then cut out abruptly
(without smoking) when the throttle is opened again. In this
case. turn the Mixture Control Screw counter-clockwise.
Mixture Control Screw adjustment is not critical and, by re-
membering the symptoms of rich and lean running quoted above.
it is a simple matter to establish the best setting.
The correct mixture for part-throttle (medium speed) running is
automatically controlled by the Mixture Control Screw when it
has been adjusted to the best idling setting.
4. If. after carrying out mixture adjustments, the idling speed is
found to be too high, the throttle trim lever should be moved
downward until the desired idling speed is achieved.
Note: Once the correct carburettor settings have been established, it
should be unnecessary to alter them. Such slight needle-valve
adjustments as may be required to cope with variations in
atmospheric conditions, will not normally affect the other
controls. A small readjustment may be required if the fuel
and/or plug are changed to different types.
SUBSEQUENT OPERATION AND CARE
It is important that the carburettor operates under perfectly clean
conditions. Make sure that fuel is properly filtered before use. We
also advise fitting a filter in the delivery tube between the tank and
engine. Foreign matter in the fuel system can reduce the flow of
fuel, thereby weakening the mixture and risking damage to the
engine by overheating. Check filters at regular intervals and remove
any dirt or fibres. It is also advisable to check the cleanliness of the
Needle Valve
Fuel inlet
Throttle Lever
Rotor Guide Screw
Mixture Control Screw