O.S. Engines 7M Carb - 27481000 - Manual

OPERATING INSTRUCTIONS FOR THE O.S.TYPE 7M CARBURETTOR
The O.S. Type 7M carburettor is an entirely new carburettor of advanced design that has been specially developed to meet the
demands of FAI F3A contest flying.
The Type 7M carburettor enables the user to adjust mixture strength separately for the idling, half-throttle and full throttle
ranges, in order to obtain optimum throttle response and complete reliability throughout the engine's operational spectrum.
Adjustment is simplified by the fact that each control works independently and does not affect response over other speed ranges.
Four adjustable controls are provided on the Type 7M
carburettor but it is quite simple to adjust. The controls are:
•The Needle-Valve: For adjusting the mixture strength when the
throttle is fully open.
•The Mid-Range Mixture Control Screw: For adjusting the mixture
strength when the throttle is set for medium speeds — i.e. the range
which is most widely used in contest flight.
•The Idle Mixture Control Screw: For adjusting the mixture strength
when the engine is running at low speeds — i.e. the range between idl-
ing speed and approximately "quarter-throttle".
•The Throttle Stop Screw: For establishing the minimum idling speed.
PROVISIONAL SETTINGS
Before starting the engine, check that the controls are set as follows:
A Open the Needle-Valve three full turns (or 1 1/2 — 2 turns if muffler
pressurized fuel feed is used) from the fully closed position.
B The Mid-Range Mixture Control Screw is factory set at approxi-
mately the best position. If the adjustment has been moved, turn
the screw clockwise until it stops, then turn back counter-clockwise
two complete turns.
C The Idle Mixture Control Screw has an eccentric head which moves
approximately one-half turn from the full rich to full lean positions.
Make sure that this is set at the mid-way position. (Fig. 1)
ADJUSTING THE CARBURETTOR RICHER
The key to quick and positive adjustment is to adjust the controls in
the following order:
LEANER
1. The Idle Mixture Control Screw
2. The Mid-Range Mixture Control Screw
3. The Needle-Valve
1) Start the engine and allow it to idle for at least five seconds with the
throttle closed.
LEANER
Now open the throttle. If the engine hesitates before picking up
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. Re-open the throttle. If the engine now puffs out a good
deal of smoke and hesitates, or even stops, this will confirm that the
mixture is too rich. To correct this condition, gradually turn the
Idle Mixture Control Screw clockwise.
If, instead of being set too rich, the Idle Mixture Control Screw is
set too lean, the engine may stop when the throttle is closed, or it
may lose speed while idling and then cut out abruptly (without
smoke) when the throttle is re-opened. In this case, turn the Idle
Mixture Control Screw in the counter-clockwise direction.
RICHER
Fig-1
Fuel Inlet
Plug Screw
cleaning the carburettor )
Throttle Slop Screw
Throttle Lever Idle Mixture
Control Screw
Stop Screw
(Do not remove except when
disassembling ihe carburettor I
Medium Speed
Range Mixture
Control Screw
Needle Valve
(High speed mixture control