O.S. Engines 2D Carb - 22481045 - Manual

O.S. 2D
OPERATIONAL INSTRUCTIONS FOR O.S. TYPE 2D CARBURETTOR
This carburettor has been designed expressly for 21 class racing engines and releases the full potential of the O.S.
MAX-21 SE-M marine engine. It has a large throat area for high peak power output, but provides for the positive throttle
response and rapid acceleration demanded of high performance racing boat engines, via an automatic mixture control
system which also ensures ease of handling for the less experienced.
FUEL SYSTEM
The somewhat violent changes in hull attitude that may
occur in rough water means that the fuel 'head' at the
carburettor can vary considerably. Therefore, it is
recommended that a muffler (silencer) pressurized fuel
feed system be used.
ADJUSTMENT
WARNING: Running the engine needlessly with the boat out of
the water, without load and without cooling water, may
damage the engine due to overheating. Therefore, always
lower the boat into the water immediately after the engine
has been started, so as to prevent over-speeding and to allow
cooling water to be forced up to the cylinder-head.
Having carried out the initial running-in ("breaking-in")
procedure as described in the engine instructions, complete
the running-in as follows:
1) Open the throttle slightly from the idling position and start
the engine, following the procedure described in the engine
instruction leaflet.
2) Lower the boat into the water, open the throttle fully and
run the boat straight ahead for 20 to 30 metres. Now return
the model and close the needle-valve 20° to 30°. Repeat the
run, taking note of the improvement in speed.
3) Continue with further runs, gradually closing the needle-valve
(20° to 30° at a time) until no further increase in speed is
obtained.
4) If the needle-valve is closed beyond the optimum setting, the
model will slow down, accompanied by visibly diminished
exhaust smoke. In this case, immediately throttle down and
return the model to shore. Re-open the needle-valve approxi-
mately one-half turn and repeat the runs until the optimum
needle setting is found.
5) Aim to have the model achieving its highest performance
after the engine has consumed about one litre of fuel. Having
found the optimum needle-valve setting, make a note of the
number of turns necessary to re-establish this from the closed
position.
6) With the engine run-in and the optimum needle-valve setting
determined, the mixture control valve (idle valve) should be
checked as follows:
7) Run the boat in the normal way, then close the throttle.
Allow it to idle for about five seconds, then abruptly re-open
the throttle fully. If, at this point, the engine puffs out a
good deal of smoke and does not accelerate smoothly and
rapidly, it is a sign that the idling mixture is too rich.
Therefore, turn the mixture control valve clockwise 1/8 to
1/4 turn (45° to 90°). Repeat the run and recheck the result.
8) If, on the other hand, the idling mixture is too lean, the
engine is likely to speed up momentarily, then cut out
abruptly when the throttle is re-opened. In this case, turn
the mixture control valve counter-clockwise 1/8 to 1/4 turn.
Carry out these adjustments patiently under actual running
conditions until the engine responds quickly and positively to
the throttle control. (Use a small screwdriver to adjust the
mixture control valve via its slotted screwhead in the centre
of the outer end of the throttle rotor.)
Note: Mixture adjustments must not be attempted under 'no-
load' conditions. Please refer to the warning at the
beginning of this section.
9) 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 unevenly.