O.S. Engines 7DV Carb - 27181000 - 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 operating conditions, the carburettor will
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.
Rotor Set-screw
Mixture Control Screw
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 peak
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.
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.