O.S. Engines 2D User 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 approximately 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.
As
with
all engines,
it
is
advisable
to
set
both
valves
slightly
on the rich side of the best rpm setting, as a safety measure.
10) When the mixture has been corrected, the idling speed will
probably increase. Readjust the throttle opening by means
of the throttle trim on the transmitter, or by screwing out
the throttle-stop screw, so that the lowest possible idling
speed, without stopping the engine, may be obtained. Adjust
the throttle-stop screw so that the engine stops (the throttle
fully closed) when the throttle trim is at the lowest position.
Remove this with
an 8mm spanner
Photograph (1)
Dirt and fibrous matter
mostly accumulate here
Photograph (2)
Nozzle
Throttle rotor hole
A
CARBURETTOR CLEANLINESS
The correct functioning of the carburettor depends on its small
fuel orifices remaining clear. The minute particles of foreign
matter that are present in any fuel can easily partially obstruct
these orifices and upset mixture strength so that engine performance becomes erratic and unreliable.
It is recommended that fuel is passed through a filter when the
tank is filled and that a good in-line filter is installed between the
fuel tank and carburettor and, furthermore, that this filter is
frequently cleaned to remove dirt and lint that accumulates on
the filter screen. Finally, occasionally remove the needle-valve
holder from the carburettor as shown in Photo (1) and extract
any remaining foreign matter that may have lodged in the location shown in Photo (2).
REALIGNMENT OF IDLE VALVE
(MIXTURE CONTROL VALVE)
In the course of making carburettor
possible that the idle valve may be inadvertently screwed in or
out too far and thereby moved beyond its effective adjustment
range. Its basic setting can be re-established as follows:
With the throttle fully open, the position of the idle valve can be
seen by looking into the intake. The basic (factory) setting is as
shown in the main sketch, i.e. with the shoulder portion 'A'
exactly at a tangent to the throttle rotor hole.
To return the idle valve to its original position, first screw in the
idle valve, while looking into the rotor hole, until the shouldered
portion comes into view — see small sketch. Then gradually un-
screw the idle valve until 'A' is precisely tangential to the rotor
hole (i.e. so that 'A' and 'B' are superimposed) as in the main
sketch.
adjustments, it is just
B
22481400
26381501
26781200
26781309
24881824
26781506
22481300
22481310
22481320
22681953
24481150
22615000
23081706
24981930
26781965
26711305
24981959
24981837
26381501
Throttle Lever
Set-screw
Carburettor Rotor
Mixture Control Valve
"0" Ring
Rotor Spring
Rotor Stop Set Screw Assembly
Rotor Stop
Rock Nut
Fuel Inlet
Carburettor Body
Carburettor Rubber Gasket
Carburettor Fixing Screw
Needle Valve Assembly
Needle Valve Holder Assembly
Ratchet Spring
Needle
"0" Ring
Set-screw
• The above specifications are subject to change without notice for improvement.
Description
6-15 3-chome Imagawa Higashisumiyoshi-ku
Osaka 546, Japan. TEL. (06) 702-0225
© Copyright 1988 by O.S. Engines Mfg. CO., Ltd. All rights reserved. Printed in Japan.
FAX.
(06)
704-2722
38909
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