O.S. Engines 7DV User Manual

INSTRUCTIONS FOR O.S. TYPE 7D-7DV AUTOMATIC CARBURETTOR

The O.S. Type 7D & 7DV 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
new O.S. mixture control system employed by this carburettor, adjustment can be made easily and accurately.

Under

average
normally function satisfactorily as factory set. Simply start the
engine in the normal way and adjust the needle valve for
maximum rpm. On closing the throttle, the engine should idle
at between 2,000 and 2,500 r.p.m. and also run steadily at all
intermediate speeds. However, different fuels and/or climatic
conditions, may require minor readustments for optimum
results.

operating

conditions,

Mixture Control Screw

the

Rotor Set-screw

carburettor

will

Needle Valve

ADJUSTING THE CARBURETTOR

Three adjustable controls are provided on this-carburettor:
(1) The Needle Valve (located on left hand side of carburettor).
(2)

The Mixture Control Screw (located on right hand side).

(3) The Throttle Rotor Set Screw (angled at rear of body).
I. The Needle Valve is used in the same way as on all model

engines i.e., for adjusting the high speed mixture strength. Start
the engine and, with the throttle fully open, gradually close the
Needle-Valve until it is running at its maximum speed.
Caution: Do not close Needle Valve to too "lean" a setting as
this will cause the engine to overheat and slow up.
Set

the

Needle

Valve

very

slightly

to

the

"rich"

side

of

the
r.p.m. setting. Make sure that the engine is fully "broken-in"
before operating it continuously at full throttle.

II.

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 continuously and steadily without further adjustment.
(a) If, however, the engine begins to idle unevenly, open the
throttle. If the engine then hesitates before picking up to full
speed, it is probable that the idling mixture is too rich. Check
this by closing the throttle again and letting the engine idle for a
little longer before again opening up. 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. Do this by
inserting a small screwdriver into the screw on the right-hand
side and turning it clockwise. About 30 degrees turn should be
sufficient.
(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 about 30 degrees counter-clockwise.

Mixture Control Screw Adjustment is not critical and by
remembering the symptoms of rich and lean running quoted

above, it is a very simple matter to establish the best setting.

peak

III.

The Throttle Rotor Set Screw is for establishing the mini-

mum idling speed. If the engine runs too fast with the throttle
closed, the Rotor Set-Screw should be turned counter-clockwise
to allow the throttle opening to be reduced.

CARBURETTOR INSERT (for Type 7D only)

Two

different
7D carburettor. A large I.D. insert is installed in the carburettor
fitted to the MAX-90FSR. A smaller I.D. one is installed in the
carburettor of the MAX-61 engine.
In the case of the MAX-90FSR, ordinary suction feed is suffici­ent to use this carburettor with the large insert. If, however,
higher power output is required for aerobatic flying, it is permis­sible to remove the insert. In this case, a muffler pressurised fuel
system should be used.

In the case of the MAX-61, a muffler pressurised fuel system
should be used on this carburettor with the smaller I.D. insert.
If higher output is required, it is permissible to replace this with
the larger insert, or to remove the insert completely, but, in
these instances, a pumped fuel supply, such as the Perry Pump
system, or Robart Super-Pumper should be employed.

Mixture Control Screw

HOW TO REMOVE THE CARBURETTOR INSERT

•Unscrew the rotor set screw and withdraw the throttle rotor.

•Remove the idle valve set-screw and carefully withdraw idle

valve.

• Extract the carburettor insert.

• Reassemble the carburettor.

sizes

of carburettor insert

* If higher output is required on the MAX-61 FSR or

MAX-61 VF engine equipped with the type 7DV
carburettor, use the optional Type 7D carburettor.

Idle Valve

are

used

with

Carburettor Insert
(for Type 7D only)

Rotor

Idle Valve Set-screw

the

Type

SUBSEQUENT OPERATION AND CARE
Once the required settings, have been established it should
unnecessary to alter them. Such slight needle valve alterations as
may be necessary to cope with differences in atmospheric condi­tions or fuels, do not affect the other two adjustments. The

engine should start readily with the throttle in the idle position.

It is important that the carburettor operates under clean condi-

tions. Make sure that fuel is properly filtered before use. We
advise fitting a filter to your fuel can and another filter in the
delivery tube between tank and engine, to reduce the risk of the
carburettor jet becoming partially clogged and upsetting running
adjustments.

PARTS LIST

Description

Carburettor Complete

Needle Valve Assembly
Rotor Set-screw Assembly

Throttle Lever
Carburettor Retainer
Carburettor Insert-L (for 90)
Carburettor Insert-S (for 61)

The specifications is subject to alteration for improvement without notice.

Code No.

7D

29081000
29081934
27181600
26881406
29081719
29081210
29081239

be

7DV

27181000
29081934
27181600
26881406

29081719

6-15 3-chome Imagawa Higashisumiyoshi-ku
Osaka 546, Japan. TEL. Osaka [phone]

108207