O.S. Engines 2S Carb - 22884020 - Manual

OPERATIONAL INSTRUCTIONS FOR O.S. TYPE 2S & 2SB CARBURETTORS
These slide-throttle type carburettors have been designed especially for 3.5 cc class racing car engines. They
release the full potential of the O.S. MAX-21 series racing car engines, providing instant throttle response,
rapid acceleration and high peak power output. The Type 2S carburettor is for track racing, while Type
2SB is for 'off-road' or 'buggy' racing.
The carburettors are intended for operation with a muffler-pressurized fuel system. Make sure that the fuel-
tank is sealed to prevent loss of pressure.
INSTALLATION OF THE CARBURETTOR
Installation procedure is as follows.
1. Remove the protective plug from the engine's intake boss.
Make sure that the carburettor retainer (cotter-pin) does
not obstruct the boss.
2. Carefully insert the carburettor, with its rubber gasket,
into the boss.
3. Press down carburettor to lightly compress rubber gasket
and secure as follows:
(a) for MAX-21 RF-B — gently rotate cotter-pin screw
until it stops, then tighten with a further one-third
turn (approx. 120°); or
( b ) f o r MAX-21 SE and MAX-21 VF engines — gently
rotate cotter-pin nut until it stops, then rotate it a
further 30 ~ 40° to tighten.
ADJUSTMENT
1) Set the needle-valve at the optimum setting as described
in the RUNNING-IN paragraph of the engine instructions
sheet.
2) With the engine running, close the throttle and allow it to
idle for about five seconds, then open the throttle fully
and abruptly. If, at this point, the engine puffs out a
good deal of smoke and the car does not accelerate
smoothly and rapidly, it is a sign that the idling mixture
is too rich. If it is found difficult to judge this response,
allow the engine to idle for a longer period, say 10~15
seconds, then again apply full throttle. If the mixture is
too rich, the engine will either emit a large quantity of
smoke or lose speed and stop. Turn the mixture control
valve (located in the side of the carburettor body opposite
the slide valve) clockwise to correct over-rich setting.
(Use a small screw-driver and adjust in increments of 30
to 45°.) If, on the other hand, the idling mixture is too
lean, the engine is likely to speed up momentarily and
then cut out abruptly when the throttle is f u l l y opened.
In this case, turn the mixture control valve counter-clock-
wise 30 to 45°.
3) Carry out adjustments patiently, under actual running
conditions, until the engine responds quickly and positive-
ly to the throttle control.
Note: Mixture adjustments cannot be made accurately under
'no load' running conditions which, in any case, are
not advised since such running carries a risk of damag-
ing the engine through over-revving.
4) With the optimum mixture control valve position, light
smoke is visible during high speed running, and the engine
revolutions increase smoothly during acceleration.
Remember that, if the engine is operated with the fuel/air
mixture slightly too lean, it will overheat and run uneven-
ly. As with all engines, it is advisable to set both valves
very slightly on the rich side of the best rpm setting, as a
safety measure.
5) If the engine runs too fast with the throttle closed, the
throttle stop screw should be turned counter-clockwise to
allow the throttle opening to be reduced.
Note: If the fuel, gear ratio or clutch engagement point are
altered, it may be necessary to re-adjust the carburettor.