O.S. Engines 7D User Manual
INSTRUCTIONS FOR THE O.S. TYPE 7D CARBURETTOR
This carburettor incorporates an automatic mixture control device which ensures that the engine receives a
correctly balanced mixture of fuel and air at all throttle settings. It provides steady revolutions and a
smooth
out.
response,
even
to
abrupt
Throttle Stop Screw
Mixture Control Screw
Needle Valve
operation
Photo (1)
of
the
1.5~2.0mm
Fig.(1)
throttle.
Adjustment,
when required,
is
very
easy
to
carry
Three adjustable controls are provided on the Type 7D
carburettor. (See photo.)
• The Needle-Valve: For adjusting the mixture strength
when the throttle is fully open.
• 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 setting the position where
the carburettor rotor is closed.
PROVISIONAL SETTING
The use of a muffler-pressurized fuel system is recommended. Open the Needle-Valve 1 1/2~2 turns from the
fully closed position before starting the engine.
ADJUSTING THE CARBURETTOR
1) Set the throttle very slightly open from the idle position
(See Fig. 1) 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 maximum
speed.*
*Warnings
(a) Do not close the Needle-Valve to too "lean" a setting, as this
will cause overheating which may result in internal damage
and reduced engine life. Set the Needle-Valve approximately
1/4 to 1/2 turn open (i.e. "rich") from the peak r.p.m. setting,
even though this will slightly reduce r.p.m. on the ground.
(b)
Make
sure
that
the
engine
is
fully
continuously at full power. (See engine instruction leaflet.)
"run-in"
before
operating it
3) Having set the Needle-Valve as described above, close the
throttle. The engine should idle steadily and continuously. (If it stops immediately, first try turning the Throttle
Stop Screw clockwise a few degrees to raise the idling
speed a little.)
(a) If, however, the engine idles unevenly and smokes a
good deal when the throttle is re-opened, before
picking up speed, it is probable that the idling mixture is too rich. In this case it will be necessary to
adjust the Mixture Control Valve by turning the
Mixture Control Screw 1 5 to 30 degrees clockwise.
(b) Alternatively, if the Mixture Control Valve is set too
lean, the engine may stop when the throttle is
closed, or it may idle for a few moments, then speed
up very slightly before coming to a stop. Re-opening
the throttle under these conditions will usually
result in the engine cutting out abruptly, without
smoking. Corrective action is to turn the Mixture
Control Screw about 1 5 to 30 degrees counter-clockwise.
Mixture Control Valve adjustment is not unduly critical,
but do not turn the screw more than 15 — 30 degrees at
a time.
Carry out adjustments progressively and patiently, re-
membering the symptoms of rich and lean running,
quoted above, until the engine responds quickly and
positively to the throttle. Do not alter the Needle Valve
setting while adjusting the Mixture Control Valve.
Warning:
For safety reasons, it is advisable to stop the engine before
carrying out adjustments to the Mixture Control Valve or
Throttle Stop Screw.
Mixture Control Screw
Do not remove this nut.
Mixture Control
Valve
Venturi Insert
Rotor
Mixture Control
Valve Set-screw
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 variations in
atmospheric conditions will not normally affect the other two
controls. Slight readjustments may be necessary for optimum
performance if different types of fuel, glowplugs or propellers
are used.
VENTURI INSERT
This carburettor is fitted with a venturi insert for general
use. If, however, higher power output is required, it is
permissable to remove the insert.
HOW TO REMOVE THE VENTURI INSERT
1. Unscrew the Throttle Stop Screw and withdraw the
throttle rotor.
2. Remove the Mixture Control Valve Set-screw and carefully withdraw Mixture Control Valve.
3. Extract the venturi insert.
4. Reassemble the carburettor.
CARBURETTOR CLEANLINESS
The correct functioning of the carburettor 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 carburettor and, furthermore,
that this filter is frequently cleaned to remove dirt and lint
that accumulates on the filter screen. Finally, occasionally
remove the needle-valve holder from the carburettor as
shown in Photo (2) and extract any remaining foreign
matter that may have lodged in the location shown in
Photo (3).
Remove this with
8mm spanner
Photo (2) Photo (3)
Dirt and fibrous matter
mostly accumulate here
Code No.
26681603
29081305
24881824
29081200
26881311
26881406
26881424
27181600
27181620
27181610
22681953
29081110
29015019
27381900
27381940
26711305
29081952
24981837
26381501
PARTS LIST
Description
Mixture Control Screw
Mixture Control Valve
"0" Rings
Throttle Rotor
Mixture Control Valve Set-screw
Throttle Lever
Universal Link
Throttle Stop Screw Assembly
Throttle Stop Screw
Throttle Stop Screw Holder Assembly
Nipple No 1
Carburettor Body
Carburettor Rubber Gasket
Needle Valve Assembly
Needle Valve Holder Assembly
Ratchet Spring
Needle
"0" Ring
Set-screw
The specifications are subject to alteration lor improvement without notice.
©Copyright 1992 by O.S. Engines Mfg. Co., Ltd. All rights reserved. Printed in Japan.
6-15 3-chome Imagawa Higashisumiyoshi-ku
Osaka 546, Japan. TEL (06) 702-0225
FAX. (06) 704-2722
60130080-19710
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