O.S. Engines 32SX User Manual

MAX-15CV-A, 25FX, 32SX

It is of vital importance, before attempting to
operate your engine, to read the general

'SAFETY INSTRUCTIONS AND WARNINGS'

section on pages 2-6 of this booklet and to strictly
adhere to the advice contained therein.

●

Also, please study the entire contents of this
instruction manual, so as to familiarize yourself
with the controls and other features of the
engine.

●

Keep these instructions in a safe place so that
you may readily refer to them whenever
necessary.

●

It is suggested that any instructions supplied
with the aircraft, radio control equipment, etc.,
are accessible for checking at the same time.

CONTENTS

SAFETY INSTRUCTIONS AND
WARNINGS ABOUT YOUR O.S. ENGINE

INTRODUCTION,
BEFORE INSTALLING THE ENGINE

BASIC ENGINE PARTS
CARBURETOR PARTS

INSTALLATION OF THE ENGINE
THROTTLE LINKAGE, SILENCER
FUEL TANK LOCATION
GLOWPLUG
FUEL, PROPELLERS
MIXTURE CONTROLS
BEFORE STARTING
STARTING

2~6

~

11

10

11
12

13~14

14
14~16
16~17

RUNNING-IN (Breaking-in)
IDLING ADJUSTMENT CHART

7

MIXTURE CONTROL VALVE ADJUSTMENT,
REALIGNMENT OF MIXTURE CONTROL VALVE

8

SUBSEQUENT STARTING PROCEDURE
SUBSEQUENT READJUSTMENT

9

CARBURETOR CLEANLINESS,
ENGINE CARE AND MAINTENANCE

GENUINE O.S. PARTS & ACCESSORIES
ENGINE EXPLODED VIEWS &

ENGINE PARTS LISTS
CARBURETOR EXPLODED VIEWS

& PARTS LISTS
ENGINE THREE VIEW DRAWING

1

17

~

19
20

21

22

23

~

25

24

26

~

29

30~31
31

~

32

SAFETY INSTRUCTIONS AND WARNINGS ABOUT YOUR O.S. ENGINE

Remember that your engine is not a "toy", but a highly efficient internal­combustion machine whose power is capable of harming you, or others, if it is
misused.
As owner, you, alone, are responsible for the safe operation of your engine, so act
with discretion and care at all times.
If at some future date, your O.S. engine is acquired by another person, we would
respectfully request that these instructions are also passed on to its new owner.

The advice which follows is grouped under two headings according to the
degree of damage or danger which might arise through misuse or neglect.

WARNINGS

These cover events which
might involve serious (in
extreme circumstances, even
fatal) injury.

NOTES

These cover the many other
possibilities, generally less obvious
sources of danger, but which, under
certain circumstances, may also
cause damage or injury.

2

WARNINGS

Never touch, or allow any object to come

•

into contact with, the rotating
propeller and do not crouch
over the engine when it is
running.

A weakened or loose propeller may

•

disintegrate or be thrown off and, since
propeller tip speeds with powerful
engines may exceed 600 feet(180 metres)
per second, it will be understood that
such a failure could result in serious
injury, (see 'NOTES' section relating to
propeller safety).

Model engine fuel is poisonous. Do not

•

allow it to come into contact with the eyes
or mouth. Always store it in a
clearly marked container and
out of the reach of children.

Model engine fuel is also highly

•

flammable. Keep it away from open flame,
excessive heat, sources of sparks, or
anything else which might ignite
it. Do not smoke or allow anyone
else to smoke, near to it.

•

Never operate your engine in an en­closed space. Model engines, like auto­mobile engines, exhaust deadly carbon­monoxide. Run your engine only in an
open area.

Model engines generate considerable

•

heat. Do not touch any part of your
engine until it has cooled. Contact with
the muffler (silencer),
cylinder head or exhaust
header pipe, in particular,
may result in a serious burn.

3

NOTES

This engine was designed for model

•

aircraft. Do not attempt to use it for any
other purpose.

Mount the engine in your model securely,

•

following the manufacturers' recommenda­tions, using appropriate screws and lock­nuts.

Be sure to use the silencer (muffler)

•

supplied with the engine. Frequent
exposure to an open exhaust may
eventually impair your hearing.
Such noise is also likely to cause
annoyance to others over a wide area.

If you remove the glowplug from the engine

•

and check its condition by connecting the
battery leads to it, do not hold the plug with
bare fingers.Use an appropriate tool or a
folded piece of cloth.

Install a top-quality propeller of the

•

diameter and pitch specified for the engine
and aircraft. Locate the propeller on the
shaft so that the curved face of the blades
faces forward-i.e. in the direction of flight.
Firmly tighten the propeller nut, using the
correct size wrench.

4

NOTES

Always check the tightness of the propeller

•

nut and retighten it, if necessary, before
restarting the engine, particularly in the
case of four-stroke-cycle engines. If a
safety locknut assembly is provided with
your engine, always use it. This will prevent
the propeller from flying off in the event of a
"backfire", even if it loosens.

If you fit a spinner, make sure that it is a

•

precision made product and that the slots
for the propeller blades do not cut into the
blade roots and weaken them.

Preferably, use an electric starter. The

•

wearing of safety glasses is also strongly
recommended.

Discard any propeller which has become

•

split, cracked, nicked or otherwise rendered
unsafe. Never attempt to repair such a
propeller: destroy it. Do not modify a propeller
in any way, unless you are highly experienced
in tuning propellers for specialized
competition work such as pylon-racing.

Take care that the glow plug clip or battery

•

leads do not come into contact with the
propeller. Also check the linkage to the
throttle arm. A disconnected linkage could
also foul the propeller.

After starting the engine, carry out any

•

needle-valve readjustments from a safe
position behind the rotating propeller. Stop
the engine before attempting to make other
adjustments to the carburetor.

5

NOTES

Adjust the throttle linkage so that the engine

•

stops when the throttle stick and trim lever
on the transmitter are fully retarded.
Alternatively, the engine may be stopped by
cutting off the fuel supply. Never try to stop
the engine physically.

Take care that loose clothing (ties, shirt

•

sleeves, scarves, etc.)do not come into
contact with the propeller.Do not carry loose
objects (such as pencils, screwdrivers, etc.)
in a shirt pocket from where they could fall
through the propeller arc.

Do not start your engine in an area

•

containing loose gravel or sand.
The propeller may throw such material in
your face and eyes and cause injury.

For their safety, keep all onlookers

•

(especially small children) well back (at
least 20 feet or 6 meters) when preparing
your model for flight. If you have to carry
the model to the take-off point with the
engine running, be especially cautious.
Keep the propeller pointed away from you
and walk well clear of spectators.

Warning! Immediately after a glowplug-

•

ignition engine has been run and is still
warm, conditions sometimes exist whereby
it is just possible for the engine to abruptly
restart if the propeller is casually flipped
over compression WITHOUT the glowplug
battery being reconnected. Remember this
if you wish to avoid the risk of a painfully
rapped knuckle!

6

INTRODUCTION

This range of engines is ideally suited to a variety

•
of R/C aircraft, including trainer, sports, aerobatic
and scale types.

A separate precision-made needle-valve unit is

•
installed at the rear, where manual adjustment is
safely remote from the rotating propeller.

Note :
With these engines, the piston will feel tight at the
top of its stroke when the engine is cold. This is
normal. The piston and cylinder are designed to
achieve a perfect running clearance when they
reach their intended running temperature.

BEFORE INSTALLING THE ENGINE

Installing the glowplug

Carefully insert plug, with
washer, fingertight only, before
final tightening with the correct
size plug wrench.

Connecting fuel tubing

Connect the short length of fuel tubing (supplied)
securely between the needle-valve outlet and
carburetor inlet as shown in the illustration on the
next page.
In the event of the tubing becoming damaged, it
should be replaced with a suitable length (as
indicated below) of best quality 5mm ODx2mm ID
silicone tubing. Use similar material to connect the
fuel inlet nipple to the fuel tank.

Length
15CV-A
25FX
32SX

7

Glow plug

44mm
38mm
44mm

Washer

BASIC ENGINE PARTS

Cylinder head

Throttle Stop
Screw

Carburetor

Throttle Lever

Fuel inlet

Crankcase

Drive Hub

Crankshaft

Propeller washer

Propeller nut

Glowplug

Beam Mount

Fuel inlet

Needle valve

Fuel outlet

Cover Plate

Silicone Tube

MAX-15CV-A

INSTALLATION OF THE CARBURETTOR

For 15CV-A

1.

Loosen the retainer screw, rotate the
carburettor to its correct position and make
sure that it is pressed well down into the
intake boss, compressing the rubber gasket,
before retightening screw.

2.

Rotate the retainer screw gently until it
stops, then tighten a further 60-90˚.
Do not overtighten the screw as this will
damage the carburettor body.

Rotate the retainer nut
gently until it stops.

8

Tighten a further 60-90˚

INSTALLATION OF THE ENGINE

Installation in the model

A typical method of beam
mounting is shown below, left.

Rigid hardwood
(e.g. maple)

At least
12mm(1/2")

15CV-A
25FX/32SX

At least
12mm(1/2")

For CZ, 15CV-A(Code No. 71909410)
For 25FX

Retaining Screw Size

15CV-A
25FX
32SX

O.S. radial motor mount
(Available as an optional extra
part. See parts list)

¡

32SX(Code No. 71908410)

3.0mm

3.0mm

3.0mm

Make sure that the mounting beams are parallel and
that their top surfaces are in the same plane.

CORRECT INCORRECT

Front view Side view

Top surfaces are in
the same plane.

Top surfaces
are not in the
same plane.

Re-align the surfaces
as necessary

Opposite
beam

Engine does not
rest firmly.

Top surfaces
are not in the
same plane.

How to fasten the mounting screws.

3mm steel nuts

Spring
washer or
lock washer

3mm
steel screw

Hardwood mounting beams

Use mounting screws of a diameter (between 3mm)
appropriate to engine size (see table left).

Tighten second nut firmly
down onto first nut.

Tighten this nut first.

Hardwood such as
cherry or maple.

Steel washer

O.S. radial motor mount
(cast aluminum)

9

3mm steel
Allen screw

Spring
washer

THROTTLE LINKAGE

Before connecting the throttle-lever/servo linkage,

•
make sure that no part of the linkage interferes with
the internal structure of the aircraft or wiring, etc.,
when the throttle is fully open or fully closed.

Set the throttle lever linkage so that the throttle ro-

•
tor is (a) fully open when the transmitter throttle
stick is fully advanced and (b) fully closed when
the throttle stick is fully retarded.
Adjustment of the throttle rotor opening at the idling
position can then be made with the throttle trim lev­er on the transmitter.
(Select throttle-lever and servo-horn hole positions
that will avoid excessive pushrod travel causing the
throttle to bind at either end.)

Note:
When adjusting the throttle lever angle, relative to

the rotor,hold the rotor at about half-way between
the open and closed positions while loosening
and tightening the fixing screw, otherwise the
rotor, rotor guide screw,throttle stop screw or
carburettor body may become burred and
damaged.

SILENCER

The exhaust outlet of the silencer can be rotated to
any desired position in the following manner:

Assembly screw

Exhaust pressure nipple

1)

Loosen the locknut and assembly screw.

2)

Set the exhaust outlet at the required position by
rotating the rear part of the silencer.

3)

Re-tighten the assembly screw, followed by the
locknut.

NOTE :
The standard expansion-chamber type silencer is

quite effective, but reduces power to some degree.

10

Cone baffle

Turn to requlred position

Exhaust outlet

Locknut

Reminder!

Model engines generate considerable heat.
Do not touch any part of your engine until
it has cooled.
Contact with the muffler (silencer), cylinder
head or exhaust header pipe, in particular,
may result in a serious burn.
Keep your hands and face away from
exhaust gas or you will suffer a burn.

FUEL TANK LOCATION

Suggested fuel tank capacities are listed opposite.
These will allow 12-13 minute flights.
Locate the fuel tank so that the top of the tank is 5­10mm (1/4-3/8") above the level of the needle-valve.

Be sure to use a pressurized fuel system by

•
connecting the muffler pressure nipple to the vent­pipe of the fuel tank.

Suggested Fuel Tank Capacities

15CV-A
25FX
32SX

Attention to tank height

approx 100cc
approx 200cc
approx 220cc

Fuel level

10mm

11

GLOWPLUG

Since the glowplug and fuel combination used may
have a marked effect on performance and reliability, it
would be worthwhile to experiment with different plug
types.
Recommended O.S. plugs are A3 and Nos. 8.
Carefully install plug finger-tight, before final tighten­ing with the correct size plug wrench.

The role of the glowplug

With a glowplug engine, ignition is initiated by the
application of a 1.5-volt power source. When the battery
is disconnected, the heat retained within the combustion
chamber remains sufficient to keep the plug filament
glowing, thereby continuing to keep the engine running.
Ignition timing is 'automatic' : under reduced load,
allowing higher rpm, the plug becomes hotter and,
appropriately, fires the fuel/air charge earlier;
conversely, at reduced rpm, the plug become cooler and
ignition is retarded.

Glowplug life

Particularly in the case of very high performance
engines,

glowplugs must be regarded as expendable
However, plug life can be extended and engine
performance maintained by careful use, i.e.:

Install a plug suitable for the engine.

•

Use fuel containing a moderate percentage of

•

nitromethane unless more is essential for racing
events.

Do not run the engine too lean and do not leave the

•

battery connected while adjusting the needle.

When to replace the glowplug

Apart from when actually burned out, a plug may
need to be replaced because it no longer delivers its
best performance, such as when:

Filament surface has roughened and turned white.

•

Filament coil has become distorted.

•

Foreign matter has adhered to filament or plug

•

body has corroded.
Engine tends to cut out when idling.

•

Starting qualities deteriorate.

•

12

FUEL

Select, by practical tests, the most suitable fuel from
among the best quality fuels available in your country
for model use. For the best performance, a fuel
containing 5% to 20% nitromethane is preferable.
Lubricants may be either castor-oil or a suitable
synthetic oil ( or a blend of both ) provided that they
are always of top quality.
For consistent performance and long engine life, it is
essential to use fuel containing AT LEAST 18%
lubricant by volume. Some fuels containing coloring
additives tend to deteriorate and may adversely affect
running qualities.
Once a satisfactory fuel has been selected and used
for a while, it may be unwise to needlessly change
the brand or type. In any engine, a change of fuel
may cause carbon deposits in the combustion
chamber or on the piston head to become detached
and lodged elsewhere, with the risk of this causing
unreliable operation for a while. If, however, the
adoption of a different fuel is unavoidable, check the
engine for the first few flights on the new fuel, by
temporarily reverting to the running-in procedure.

Reminder!

Reminder!

Model engine fuel is poisonous. Do
not allow it to come into contact with
the eyes or mouth. Always store it in a
clearly marked container and out of
the reach of children.

Model engine fuel is also highly flam­mable. Keep it away from open flame,
excessive heat, sources of sparks, or
anything else which might ignite it.
Do not smoke, or allow anyone else to
smoke, near to it.

PROPELLERS

Suggested propeller sizes are listed on page 14. The
suitability of the prop depends on the size and weight
of the model and type of flying. Determine the best
size and type after the engine has been run in. Check
the balance of the propeller before fitting it to the
engine. Unbalanced propellers cause vibration and
loss of power. Wooden propellers are to be preferred.
Some nylon propellers are not strong enough to
withstand the high power output of these engines
and a thrown blade can be very dangerous.

13

Sport

15CV-A
25FX
32SX

Reminder!

8✕4~6,8✕4~6,9✕4

✕

9

5~6,9.5✕5,10✕5

✕

10

6,10.5✕5,11✕6

Never touch, or allow any object to come
into contact with, the rotating propeller and
do not crouch over the engine when it is
running.

Aerobatic

8✕4~6

✕

6,9.5✕5

9

✕

7~8,10✕6

9

•

The Mixture Control Valve (carburetor)

This meters fuel flow at part-throttle and idling
speeds to ensure reliable operation as the throttle
is opened and closed. The Mixture Control Valve is
factory set for the approximate best result. First run
the engine as received and readjust the Mixture
Control Screw only if necessary.

Type of Carburetor

15CV-A
25FX
32SX

10K
20D
20F

MIXTURE CONTROLS

Two mixture controls are provided on these
engines.

The Needle Valve (at rear of engine)

•
When set to produce maximum power at full
throttle, this establishes the basic fuel/air mixture
strength. The correct mixture is then maintained by
the carburetor's built-in automatic mixture control
system to cover the engine's requirements at
reduced throttle settings.

BEFORE STARTING

Tools, accessories, etc.

The following items are necessary for operating the
engine.

1 Fuel

Model glowplug engine fuel of good quality, preferably
containing a small percentage of nitromethane.

2 Glowplug

O.S. A3 and No.8 glowplug is fitted to the engine.

3 Propeller

Suggested size is 7x5-6(15CV-A), 9X5-6 (25FX), or
10X6 (32SX).

14

4 Glowplug battery

The power source for heating the glowplug may be
either a large heavy-duty 1.5volt dry cell, or preferably,
a 2-volt rechargeable lead-acid cell (accumulator).

If a 2-volt cell is employed,
use a resistance wire, as
shown, to reduce applied
voltage, otherwise element

1.5 volt heavy-duty
dry battery

or 2 volt rechargeable
lead-acid cell (at least 5Ah)

will overheat and burn out.

Warning (Very hot)

Never touch the nichrome wire while the battery is
connected.

Resistance coil
(nichrome wire)

Battery leads

Adjust applied voltage by changing the position of clip on
resistance coil until glowplug element is glowing bright red.

Raise

voltage to

increase

brightness.

Lower voltage to

reduce brightness.

5 Battery leads

Battery leads

These are used to conduct current
from the battery to the glowplug.
Basically, two leads, with clips, are
required, but, for greater conve­nience, twin leads with special glowplug connectors,
as shown on the right, are commercially available.

6 Fuel tank

For installation in the model, a 100cc(3.5oz.) for 15CV­A, a 200cc(7oz.) for 25FX, a 240cc(8.5oz.) for 32SX
tank, is suggested.

7 Fuel bottle or pump

For filling the fuel tank, a simple,
polyethylene "squeeze" bottle, with
a suitable spout,is all that is
required. Alternatively, one of the
purpose-made manual or electric

Fuel pumps

fuel pumps may be used to transfer
fuel directly from your fuel
container to the fuel tank.

Electric

8 Electric starter and starter battery

An electric starter is recommended
for starting.

12V Battery

15

Fuel bulb

Manual

Starter

9 Fuel can filter

Fit a filter to the outlet tube of your

Fuel Can Filter

refuelling container to prevent entry
of foreign matter into the fuel tank.

10 Silicone tubing

This is required for the
connection between the fuel
tank and engine.

11 Plug wrench

Used for tightening glowplug. The
O.S. long plug wrench is available
as an optional accessory.

For tightening
glowplug

STARTING

1.

Install appropriate propeller and tighten securely.

2.

To facilitate electric starting, Install an O.S. solid
aluminium alloy spinner-nut for centering the rubber
drive insert of the starter. Alternatively, a good
quality spinner, enclosing the propeller boss, may be
used, but make sure that it is of precision-made and
sturdy construction so that the spinner shell cannot
loosen when the starter is used. Close the throttle.

Fill the fuel tank. Do not allow fuel to overflow into

3.
the silencer, otherwise the engine may become
flooded and difficult to start.

Check that the needle-valve is closed. (Do not

4.
overtighten.) Now open the needle-valve counter­clockwise to the starting setting:-

1

2

~

3 turns for 15CV-A

•

2

1

~

2 turns for 25FX

1

•

2

1

1 turns for 32SX

•

2

Mark

Turn needle-valve clockwise to close
(for leaner mixture)

Turn needle-valve counter-clockwise

Close

to open (for richer mixture)

Open

5. Open the throttle approx. one-quarter.

(This is to avoid unnecessarily
high r.p.m. when the engine starts.)

Fully closed
position

1
4

Fully opened position

3
4

Set at this point

16

6. Connect battery leads to glowplug.
Bring electric starter into contact with spinner-nut

7.

or spinner and depress starter switch for one or
two seconds. Repeat if necessary.
When the engine starts, withdraw the starter im­mediately.

Attention :
Do not choke the carburettor air intake when applying
the starter. This could cause an excessive amount of
fuel to be drawn into the cylinder which may initiate
an hydraulic lock and damage the engine.
If the engine does not start within 10 repeat
applications of the starter, remove the glow-plug,
check that it glows brightly and that the cylinder is not
flooded with fuel. (To eject excess fuel, close needle­valve and apply starter with glowplug removed.) Then
try again.

VERY IMPORTANT!

Before being operated at full power (i.e. at full-throttle and
with the needle-valve closed to its optimum setting) the
engine must be adequately run-in, otherwise there is a
danger of it becoming overheated and damaged.

RUNNING-IN ("Breaking-in")

All internal-combustion engines benefit from extra
care when they are run for the first few timesknown
as running-in or breaking-in.
This allows the working parts to mate together under
load at operating temperature. Therefore, it is vitally
important to complete the break-in before allowing the
engine to run continuously at high speed and before
finalizing carburetor adjustments.
However, because O.S. engines are produced with
the aid of the finest modern precision machinery and
from the best and most suitable materials, only a
short and simple running-in procedure is called for
and can be carried out with the engine installed in the
model. The process is as follows.

Install the engine with the propeller intended for

1.
your model. Open the needle-valve to the advised
starting setting and start the engine. If the engine
stops when the glow plug battery disconnected,
open the needle-valve to the point where the en­gine does not stop.Run the engine for one minute
with the throttle fully open, but with the needle­valve adjusted for rich, slow "four-cycle"operation.

17

2.

Now close the needle-valve until the engine
speeds up to "two-cycle"operation and allow it to
run for about 10 seconds, then reopen the needle­valve to bring the engine back to "four­cycle"operation and run it for another 10 seconds.
Repeat this procedure until the fuel tank is empty.

Re-start and adjust the needle-valve so that the

3.
engine just breaks into "two-cycle" from "four­cycle" operation, then make three or four flights,
avoiding successive "nose-up" flights.

4.

During subsequent flights, the needle-valve can be
gradually closed to give more power.
However, if the engine shows signs of running too
lean, the next flight should be set rich. After a total
of ten to fifteen flights, the engine should run
continuously, on its optimum needle-valve setting,
without loss of power as it warms up.

5.

After the completion of the running-in adjust the
carburetor at optimum setting referring to
MIXTURE CONTROL VALVE ADJUSTMENT
section and SUBSEQUENT READJUSTMENT
section.

Optimum needle setting(1)

Slowly advance the throttle to its fully open position,
then gradually close the needle-valve until the
exhaust note begins to change. (4-cycle to 2-cycle)
At this point, disconnect the battery from the
glowplug, taking care that the battery leads or
glowplug clip do not come into contact with the
rotating propeller. If the engine stops when the
battery is disconnected, close the needle-valve about
30˚ and restart.

Optimum needle setting(2)

As the needle-valve is closed slowly and gradually,
the engine r.p.m. will increase and a continuous high­pitched exhaust note, only, will be heard. Close the
needle-valve 10-15˚ and wait for the change of r.p.m.
After the engine r.p.m. increases turn the needle­valve another 10 -15˚ and wait for the next change of
r.p.m. As the speed of the engine does not instantly
change with needle-valve readjustment, small move­ments, with pauses between, are necessary to arrive
at the optimum setting.

18

Needle-valve adjustment diagram

6

Clear, high-pitched two-stroke
exhaust note

5

Intermittent, high-pitched
two-stroke note
superimposed
on low "four-stroke"
sound.

4

Disconnect battery
leads from glowplug at
about this point.

3

Exhaust note starts to change.

Note: Although this is a two-stroke engine it fires like a
four-stroke at these rich needle-valve settings-i.e. ignition
of the fuel charge takes place at every fourth stroke of the
piston instead of at every second stroke.

Practical best(optimum) needle-valve setting

E

n

g

e

i

n

s

t

o

s

p

20

~

7

45˚

Maximum rpm
setting("Lean").

1

STARTING

t

t

r

e

"Rich" needle-valve

a

d

t

s

setting when starting

o

t

s

.

the engine.

n

e

o

s

i

t

a

u

e

l

r

o

c

v

e

e

d

R

o

t

2

The engine may stop if
the battery leads are
disconnected from the
glowplug while the
engine is running rich.

19

Note :
This diagram is for reference

purposes only.
Actual needle positions may
differ from those shown.

To stop the engine, close the

•
throttle completely to cut off
fuel/air supply.

IDLING ADJUSTMENT CHART

Re-set the idling position at
a little higher r.p.m.

20

Refer to the next section.

Engine stops.

Engine stops.

Engine stops.

Start the engine.

Make sure that the throttle is
fully open.

Adjust the neede-valve.

Close the throttle gradually.

Find the idling position.

Fix the idling position.

Open the throttle fully.

Does the engine
regain full power?

Continue running at high speed
for 10 seconds.

Close the throttle.

Run at idling speed for 5 seconds.

Does the engine stop?

Apply full throttle.

Does the engine

regain full power immediately?

OK

Yes.

No.

Yes.

Disconnect the battery
leads at mid speed.

20-30˚ open from maximum
r.p.m. setting.

The position where the lowest
possible r.p.m. ,with steady
running, is obtained.

Set the throttle opening by
means of the throttle trim on
the transmitter so that the lowest
practical speed, without risk of
the engine stopping,is obtained.

MIXTURE CONTROL VALVE ADJUSTMENT

With the engine running, close the throttle and allow it
to idle for about five seconds, then open the throttle
fully. If, at this point, the engine is slow to pick up and
produces an excess of exhaust smoke, the mixture is
too rich. Correct this condition by turning the Mixture
Control Screw clockwise 15-30˚. If the mixture is
excessively rich, engine rpm will become unstable:
opening the throttle will produce a great deal of
smoke and rpm may drop suddenly or the engine
may stop. This condition may also be initiated by
excessively prolonged idling.
If,on the other hand, the mixture is too lean, this will
be indicated by a marked lack of exhaust smoke and
a tendency for the engine to cut out when the throttle
is opened. In this case, turn the Mixture Control
Screw counter-clockwise 90˚to positively enrich the
idle mixture, then turn the screw clockwise gradually
until the engine regains full power cleanly when the
throttle is reopened.
Carry out adjustments patiently until the engine
responds quickly and positively to the throttle control.

Note: Mixture Control Valve adjustments should

be made in steps of 15-30˚ initially,
carefully checking the effect, on throttle
response, of each small adjustment.

REALIGNMENT OF MIXTURE CONTROL VALVE

In the course of making carburetor adjustments, it is
just possible that the Mixture Control 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:
Close the throttle rotor gradually from the fully
opened position until it is just fully closed.
(Do not turn further.) Then, screw in the Mixture
Control Screw until it stops. Now unscrew the Mixture
Control Screw as indicated below.

2

15CV-A
25FX
32SX

21

approx 1 turns

3

1

approx 1 turns

2

1

approx 3 turns

2

SUBSEQUENT STARTING PROCEDURE

Once the optimum needle-valve setting has been es­tablished (see page 19, Needle-valve adjustment dia­gram) the procedure for starting may be simplified as
follows.

Open the needle-valve one half-turn (180°) from

1.
the optimum setting.

Set the throttle one-quarter open from the fully

2.
closed position, energize the glowplug and apply
the electric starter. When the engine starts, re­open the throttle and re-adjust the needle-valve to
the optimum setting.

Note:
When re-starting the engine on the same day,
provided that atmospheric conditions have not
changed significantly, it may be practicable to re­start the engine on its optimum(running) setting.

SUBSEQUENT READJUSTMENT

Once the engine has been run-in and the controls
properly set up, it should be unnecessary to alter the
mixture settings; except to make minor adjustments
to the Needle-Valve occasionally, to take account of
variations in climatic conditions.
The use of a different fuel, however, particularly one
containing more, or less, nitromethane and/or a
different type or proportion of lubricating oil, is likely to
call for some readjustment of the Needle-Valve.
Remember that, as a safety measure, it is advisable
to increase the Needle-Valve opening by an extra
half-turn counter-clockwise, prior to establishing a
new setting. The same applies if the silencer type is
changed.
A different silencer may alter the exhaust pressure
applied to the fuel feed and call for a revised Needle­Valve setting. The use of a different glowplug may
also require compensating carburetor readjustments.

22

CARBURETOR CLEANLINESS

The correct functioning of the carburetor 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.
O.S.'Super-Filters'(large and small ) are available, as
optional extras, to deal with this problem.
One of these filters, fitted to the outlet tube inside
your refueling container, will prevent the entry of
foreign material into the fuel tank.
It is also recommended that a good in-line filter be
installed between the tank and needle-valve.
Do not forget to clean the filters regularly to remove
dirt and lint that accumulate on the filter screen.
Also, clean the carburetor itself occasionally.

ENGINE CARE AND MAINTENANCE

At the end of each operating session, drain out any

1.
fuel that may remain in the fuel tank.

Next, energize the glowplug and try to restart the

2.
engine to burn off any fuel that may remain inside
the engine. Repeat this procedure until the engine
fails to fire. Remove the glowplug and eject any re­sidue by rotating the engine with an electric starter
for 4 to 5 seconds while the engine is still warm.

Finally, inject some after-run oil into the engine.

3.
Rotate the engine a few times by hand, to make
sure that it is free, and then with an electric starter
for 4 to 5 seconds to distribute the oil to all the
working parts.

Note:
Do not inject after-run oil into the carburetor as
this may cause the O-ring inside the carburettor
to deteriorate.

These procedures will reduce the risk of starting
difficulties and of internal corrosion after a period of
storage.

23

O.S. GENUINE PARTS & ACCESSORIES

O.S. GLOW PLUGS

■

No.8

(71608001)

A5

(71605100)

A3

(71605300)

SILENCER EXTENSION

■

ADAPTORS

Type of Engine • Silencer

Code No.

21125108
22625103
23325100

15CV-A(871)

25FX(892)

32SX(E-3030

SPINNER NUT

■

Code No.

20824005
23024008
23024009

)

Type of Engine

Size

M5

1/4"-28

1/4"-28(L

15CV-A

20. 25. RE

25FX. 32SX

)

SILENCER EXHAUST

■

ADAPTORS

Code No. Type of Engine • Silencer

21125502
22625508

15CV-A(871)

25FX(892) 32SX(E-3030)

24

LONG PROPELLER NUT SETS

■

Code No. Size Type of Engine

73101000 1/4"-28

PROPELLER NUT SETS

■

25FX. 32SX

FOR TRUTURN SPINNERS

(73101020)

For 25FX.32SX

SUPER SILENCERS

■

SUPER FI LTER

■

(72403050)

■

LOCK WASHER

(10Sets)

Type of Engine

Code No.

23325030 E-3030S 32SX

■

Size

NON-BUBBLE WEIGHT

(71531000)

LONG SOCKET WRENCH

■

WITH PLUG GRIP

(71521000)

25

Code No.

55500002 25FX.32SX

Type of Engine

Size

M3

EXPLODED VIEW (15CV-A)

C.M2.6x12

1

2

26

3

4

5

6

-

0

9

8

7

✽

Type of screw

q

C…Cap Screw F…Flat Head Screw N…Round Head Screw S…Set Screw

w

M.M2.6x8

=

e

-1

r

S.3x3

e

-2

e

-4

e

-5

e

-3

e

ENGINEN PARTS LIST (15CV-A)

No.

Code No.

2 1504 010

1

2 1503 010

2

2 1706 000

3
4

2 1205 040
2 1581 000

5

2 1481 700

6

2 0810 007

7
8

2 1109 005

9

2 1408 000

0

2 2631 019

-

2 1501 020

=

2 1230 000
2 1502 000

q

27

w

e
e
e
e
e
e

r

-1

-2

-3

-4

-5

2 1514 010
2 1507 000
2 1507 100
2 6711 305
2 1781 970
2 4981 837
2 6381 501
2 1513 000
7 1605 300
2 1225 000
2 2681 957
2 2325 300
2 1225 500

Specifications are subject to alteration for improvement without notice.

Cylinder Head
Cylinder & Piston Assembly
Piston Pin
Connecting Rod
Carburetor (Type 10K)

Carburetor Retainer
Propeller Nut
Propeller Washer
Drive Hub

Crankshaft Ball Bearing (Front)
Crankcase
Crankshaft Ball Bearing (Rear)
Crankshaft

Gasket Set

Cover Plate Assembly

Cover Plate Body

Ratchet Spring

Needle

"O"

Screw Set

Glow Plug A3
871 Silencer

Exhaust Pressure Nipple

Assembly Screw
Retaining Screw (2pcs.)

Description

Ring For Needle (2pcs.)

Set Screw

EXPLODED VIEW (25FX,32SX)

C.M2.6X12

1

2

28

5

5

-1

5

-2

9

8

7

6

✽ Type of screw

C…Cap Screw F…Flat Head Screw N…Round Head Screw S…Set Screw

3

4

-

N.+M3.5X5

0

q

w

C.M2.6X7

=

e

-2

e

-1

e

r

S.M3X3

e

-7

e

-5

e

-4

e

-6

e

-3

ENGINEN PARTS LIST (25FX,32SX)

25FX

22604020
22603040
22606009
22805010
22681030

22615000
23081706
23210007
23009006
22808000
22620003
22831000
22601050
22630002
22602030
22614010
22607010
22607011
22681953
22681980
24981837
26381501
27381940
26711305
22413009
22628000

22681957
23325300
22625404

Code No.

29

5
5

e
e
e
e
e
e
e

No.

1
2
3
4
5

-1

-2

6
7
8
9
0

­=
q
w
e

-1

-2

-3

-4

-5

-6

-7

r

Description

Cylinder Head
Cylinder & Piston Assembly
Piston Pin

Connecting Rod
Carburetor (Type 20D )
Carburetor (Type 20F )

Carburetor Rubber Gasket

Carburetor Retaining Screw(2pcs.)
Propeller Nut(UNF1/4-28)
Propeller Washer
Drive Hub
Thrust Washer
Crankshaft Ball Bearing (Front)
Crankcase
Crankshaft Ball Bearing (Rear)
Crankshaft
Gasket Set
Cover Plate Assembly

Cover Plate Body

Nipple No.1

Needle

"O"Ring For Needle (2pcs.)

Set Screw

Needle Valve Holder Assembly

Ratchet Spring
Screw Set
892 Silencer (For 25FX)
E-3030 Silencer (For 32SX)

Exhaust Pressure Nipple

Assembly Screw
Retaining Screw (2pcs.)

Specifications are subject to alteration for improvement without notice.

32SX

23404100
23403000
23406000
23405000

23482000
22615000
23081706
23210007
23009006
22808000
22620003
22831000
23401000
23430000
23402100
23414000
23407000
23407100
22681953
22681980
24981837
26381501
27381940
26711305
22413009

23325020
22681957
23325320
22625404

CARBURETOR 10K (15CV-A)

5

1

2

3

4

✽ Type of screw

C…Cap Screw F…Flat Head Screw
N…Round Head Screw S…Set Screw

No.

1
2
3
4
5
6
7
8

Code No.

2 2681 430
2 1284 200
2 1284 600
2 2481 506
2 1581 100
2 2681 320
2 2681 953
2 2615 000

Throttle Lever Assembly
Carburettor Rotor
Mixture Control Screw (W/O-Ring)
Rotor Spring
Carburettor Body
Throttle Stop Screw
Fuel Inlet (W/Washer)
Carburetor Rubber Gasket

Description

Specifications are subject to alteration for improvement without notice.

6

7

8

30

No.

1

1

1

-1

Code No.

1

22681430

-1

22681419

2

22681220

3

22681600

4

22481506

5

22681140

6

22681320

7

22681953

8

22615000

9

23081706

CARBURETOR 20D (25FX)

2

3

4

5

N.+M3.5X5

8

9

Description

Throttle Lever Assembly
Throttle Lever
Carburettor Rotor
Mixture Control Screw (W/O-Ring)
Rotor Spring
Carburettor Body
Throttle Stop Screw
Fuel Inlet (W/Washer)
Carburetor Rubber Gasket
Carburettor Retaining Screw

6

7

No.

1
1-2

5

CARBURETOR 20F (32SX)

1-21

-1

1

2

3

Code No.

1

22781401

-1

22781420
22781411

2

23481200

3

23481650

4

26781506

5

23482100

-1

24881824

6

45581820

7

22681953

8

22615000

9

23081706

5

5

-1

4

N.+M3.5X5

9

Description

Throttle Lever Assembly
Throttle Lever Fixing Screw
Throttle Lever
Throttle Rotor
Mixture Control Valve Spring
Rotor Spring
Carburettor Body
"O"Ring (2pcs.)
Rotor Guide Screw
Fuel Inlet (W/Washer)
Carburetor Rubber Gasket
Carburetor Retaining Screw

6

7

8

THREE VIEW DRAWING

MAX

15CV-A

-

Displacement

■

Bore

■

Stroke

■

Practical R.P.M.

■

Power output

■

Weight

■

25
39

SPECIFICATIONS

2.49 cc (0.152 cu.in.

15.2mm (0.598 in.

13.7mm (0.539 in.

~

19,000 r.p.m.

2,500

0.5 bhp / 18,000 r.p.m.
170g (5.99 oz.

M5

49.513

)

4-ø3.3

21

)
)
)

31.4

11

27.5

14.5

13

25

19.8

17.5

41

25.5

31

THREE VIEW DRAWING

SPECIFICATIONS

Displacement

■

Bore

■

Stroke

■

Practical R.P.M.

■

Power output

■

Weight

■

4.07 cc (0.2485 cu.in.

18.0mm (0.7087 in.

16.0mm (0.630 in.

~

19,000 r.p.m.

2,500

0.84 bhp / 18,000 r.p.m.
248g (8.75 oz.

)

)

)

MAX

)

25FX

­SPECIFICATIONS

Displacement

■

Bore

■

Stroke

■

Practical R.P.M.

■

Power output

■

Weight

■

Dimensions(mm)

MAX

5.23 cc (0.319 cu.in.

19.5mm (0.768 in.

17.5mm (0.689 in.

~

2,000

1.2 bhp / 18,000 r.p.m.
270g (9.5 oz.

)
)

22,000 r.p.m.

)

)

15 4-ø3.3

32SX

-

38

4-ø3.3

15

35

19

16

60

1/4-28UNF

30.5

22.3

15.5
24

53

30

46

22.6

24.8

30.6
45

UNF1/4-28

22

35

16 19

53

38

57.2

30.5

22

15.3

22.7

24.8

32

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Copyright 2000 by O.S.Engines Mfg. Co., Ltd. All rights reserved. Printed in Japan.

E

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F

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S

6-15 3-Chome Imagawa Higashisumiyoshi-ku
Osaka 546-0003, Japan

URL : http://www.os-engines.co.jp

TEL.[phone]

FAX. [phone]

110101