O.S. Engines 29381010 User 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

Needle Valve

Fuel inlet

Throttle Lever

Rotor Guide Screw

Mixture Control Screw

• Make sure, when the engine is installed in the aircraft or
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

2. In the case of a marine installation, put the boat on the water

3. The Mixture Control Screw is for adjusting fuel mixture strength

4. If. after carrying out mixture adjustments, the idling speed is

Note: Once the correct carburettor settings have been established, it

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 com­ponents as the cylinder, piston, connecting-rod, etc. will
be seriously damaged if they are allowed to become over­heated.

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.

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 re­opening 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 re­membering 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.

found to be too high, the throttle trim lever should be moved
downward until the desired idling speed is achieved.

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.

boat,

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

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

fitting a filter

in

the

delivery tube between the tank and

Set-screw

carburettor periodically. Using the wrench supplied, remove the
needle-valve holder from the carburettor body and wash out the
interior to remove any minute particles that may have escaped
through the filters.

Dirt and librous matter mostly

Remove this with an 8mm wrench

accumulate here

Fixing nut

Model or fitting plate

Ratchet spring

Remote needle holder

Needle

Needle knob

Silicone tubing

Plug screw

Needle-valve control lever

Remote needle holder

REALIGNMENT OF MIXTURE CONTROL SCREW

The Mixture Control Screw is factory set at the approximate best

position. If, however, the Mixture Control Screw has been
tampered with, or moved accidentally, set it at the original position

as follows. Screw in the Mixture Control Screw until it stops while

keeping the rotor fully closed. Then. unscrew 2-1/2 turns. This is the
original position of the Mixture Control Screw.

Needle Control Lever

By fitting the Needle Control Lever (supplied) to the needle knob,
the needle-valve can be adjusted by radio-control. Before fitting the

Lever, remove the needle ratchet spring.

Type 9B Remote-mounting Needle Valve Assembly

This is an optional extra part. It enables the Needle Valve to be
installed separately from the engine in a position where (especially
with a cowled or enclosed engine) it may be more accessible for
adjustment. (See sketch.) Install as follows:

• Remove the needle-valve holder from the carburettor and fit the
plug screw in its place.

• Drill a 6mm dia. hole in the required position on the model and
insert the Remote Needle Valve Assembly. If necessary, install a
suitable mounting plate in the model to which the Remote
Needle Valve Assembly may be fitted.

• For piping, use heavy-duty silicone tubing of at least 2mm bore
and 5mm outer diameter. Tube length should be kept as short as
possible.

• You may also use the Needle Control Lever in conjunction with

the Remote-mounting Needle Valve Assembly.

PARTS LIST

Description

28282300
28281900
28281970
24981837
26381501
27381940
26711305
28281110
29315000
28281500
28281200
28281210

28281300
27881820
28281400
22681953
24925202
28281600

The specifications are subject to alteration (or improvement without notice.

Needle Control Lever
Needle Valve Assembly
Needle

"0" Ring(2pcs.)
Set-Screw
Needle Valve Holder Assembly
Ratchet Spring
Carburettor Body
Carburettor Rubber Gasket
Rotor Spring

Carburettor Rotor
Carburettor Insert
Mixture Control Screw

"0" Ring(2pcs.)

Throttle Lever Assembly
Fuel Inlet
Carburettor Fixing Screw
Rotor Guide Screw

6-15 3-Chome Imagawa Higashisumiyoshi-ku
Osaka 546-0003. Japan TEL. [phone]

FAX [phone]