O.S. Engines 21XZ-R User Manual

It is of vital importance, before attempting to operate
your eng ine, to read the gene ral 'SA FETY
INSTRUCTIONS AND WARNINGS' section on
pages 2-5 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 vehicle, radio control equipment, etc., are
accessible for checking at the same time.

1

CONTENTS

SAFETY INSTRUCTIONS AND
WARNINGS ABOUT YOUR O.S. ENGINE

ENGINE CONSTRUCTION, NOTES WHEN
APPLYING AN ELECTRIC STARTER

NOTES ON OPERATION,
ABOUT THE ENGINE

TOOLS, ACCESSORIES, etc.
BASIC ENGINE PARTS

INSTALLATION OF THE STANDARD
ACCESSORIES, GLOWPLUG

INSTALLATION,
CARBURETOR CONTROLS 21M

2-5

6-7

8-9

13-14

15-17

18-22

STARTING THE ENGINE & RUNNING-IN
('Breaking-in)

FINAL ADJUSTMENT

CARE AND MAINTENANCE

TROUBLE SHOOTING

ENGINE EXPLODED VIEW &PARTS LIST

CARBURETOR EXPLODED VIEW &PARTS LIST

O.S. GENUINE PARTS & ACCESSORIES

THREE VIEW DRAWING

MEMO

36

10-12

37

26-27

28-31

32-33

23-25

34-35

38

2

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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.

SAFETY INSTRUCTIONS AND WARNINGS ABOUT YOUR O.S. ENGINE

The advice which follows applies basically to ALL MODEL ENGINES and is
grouped under two headings according to the degree of damage or danger
which might arise through misuse or neglect.

WARNINGS

NOTES

Th e se co v er ev e nts wh ich
mig h t inv o l ve se r ious (in
extreme circumstances, even
fatal) injury.

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

3

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WARNINGS

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 an 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
carbon-monoxide. 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.

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4

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This engine is intended for model cars.
Do not attempt to use it for any other
purpose.

Mount the eng ine in your model
securely, following the manufacturers'
recommendations, using appropriate
screws and locknuts.

Install an effective silencer (muffler).
Frequent close exposure to a noisy
exhaust (especially in the case of the
more powerful highspeed engines)
may eventually impair your hearing
and such noise is also likely to cause
annoyance to others over a wide area.

The wearing of safety glasses is also
strongly recommended.

Take care that the glowplug clip or
battery leads do not come into contact
with rotating parts. Also check that the
linkage to the throttle arm is secure.

For their safety, keep all onlookers
(especially small children) well back
(at least 20 feet or 6 meters) when
preparing your model for running.

NOTES

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5

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NOTES

To stop the engine, fully retard the
throttle stick and trim lever on the
transmitter, or, in an emergency, cut
off the fuel supply by pinching the fuel
delivery line from the tank.

•

Warning! Immediately after a glowplug­ignition engine has been run and is still
warm, conditions sometimes exist
whereby it is just possible for the engine
to abruptly restart if it is rotated over
compression WITHOUT the glowplug
battery being reconnected.

•

Before starting the engine, always check
the tightness of all the screws and nuts
especially those of joint and movable
parts such as throttle arm. Missing
retightening the loose screws and nuts
often causes the parts breakage that is
capable of harming you.

6

Piston

Cylinder Liner

Crankshaft

ENGINE CONSTRUCTION

With this engine, the piston will

feel tight at the top of its stroke

(TDC) when the engine is cold.

This is normal. The cylinder bore

has a slight taper. The piston

and cylinder are designed to

achieve a perfect running

clearance when they reach

operating temperature.

Near TDC

Slight taper

When the engine is cold.

When the engine is hot.

7

NOTES WHEN APPLYING
AN ELECTRIC STARTER

Do not over-prime. This could
cause a hydraulic lock and damage
the engine on application of the
electric starter.

If over-primed, remove glowplug,
close needle-valve and apply
starter to pump out surplus fuel.
Cover the head with a rag to
prevent any pumped out fuel from
getting into your eyes.

8

Please do not run on a public street, this
could cause serious accidents, personal
injuries and/or propetry damage.

Please do not run near pedestrians or
small children.

Please do not run in small or confined
areas.

Please do not run where loud noises can
disturb others, such as hospitals and
residential areas.

While Operating

GUARANTEE

This engine is constructed from the very
best materials available and to the very
highest engineering standards, using
the most advanced precision machinery.
However, the extremely high stresses
imposed by car racing operation under
very severe conditions, as well as
stresses which are exacerbated by the
use of powerful fuels containing very
high concentrations of nitromethane,
constitute hazards which are beyond a
manufacturer's control. Accordingly, we
regret that it is not possible to extend
our usual warranty terms to this
particular engine -i.e. no guarantee is
offered against material wear, or damage
resulting from, actual use.

As delivered, the engine has the
carburetor lightly fit into its intake.
Secure it changing its angle according
to the car chassis.

NOTE

NOTES ON OPERATION

9

Standard accessories

Glow Plug RP7
T-type head (Turbo head) 1piece

Exhaust Seal Ring 1piece

ABOUT THE ENGINE

Cylinder-head gasket
(0.2mm) 1 piece

Dust Cap 3, 16, 18 1piece each

Caburetor Reducer 9mm
(Blue) 1piece

Flywheel No.1E Collet 1piece

The MAX-21XZ-R is expressly designed for 1/8
On-Road Racing. All the major parts are newly
designed. Crankshaft passenger port is filled
with silicone for increased intake efficiency and
two tungsten weights are pressed into the
counterweight for increased torque and mid
speed. Cylinder liner has seven scavenging
ports and three exhaust ports for increased
combustion efficiency. Combustion chamber
and carburetor are newly designed to best
match these parts. Also, better balanced
stronger connecting rod and lighter weight
piston are employed. O.S. standard of easy to
handle characteristics and high performance
have been realized.

10

GLOWPLUG IGNITER

Commercialy available handy
glowplug heater in which the
glowplug battery and battery
leads are integrated.

FUEL

Generally, it is suggested that the user selects a fuel
that is commercially available for model two-stroke
engines and contains 10-30% nitromethane. As a
starting point, we recommend a fuel containing 20%
nitromethane, changing to a fuel containing more
nitro if necessary. When the brand of fuel is changed,
or the nitro content increased, it is advisable to
repeat the running-in procedure referred to in the
RUNNING-IN paragraphs. Please note that with
high-nitro fuels, although power may
be increased for competition purposes,
glowplug elements do not last as long
and engine life will be shortened.

Items necessary for starting

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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.

TOOLS, ACCESSORIES, etc.

The following items are necessary for operating the engine.

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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.

FUEL FILTER

To be installed in the fuel line
between fuel tank and carburetor
to prevent dust from entering the
carburetor.

STARTER BOX

For starting the engine.

11

FUEL PUMP

For filling the fuel tank, a simple,
polyethylene "squeeze" bottle,
with a suitable spout, is required.

SILICONE FUEL LINE

Heatproof silicone tubing of
approx. 5mm o.d. and 2mm i.d. is
required for the connection
between the fuel tank and engine.

TOOLS

HEX SCREWDRIVER

SCREWDRIVER

Necessary for engine installation.

1.5mm, 2mm, 2.5mm, 3mm

Necessary for carburetor adjustments.
No.1, No.2, etc

LONG SOCKET WRENCH WITH PLUG GRIP

Recommended for easy removal and
replacement of the angled and recessed
glowplug, the O.S.Long Socket Wrench
incorporates a special grip.

BATTERIES FOR STARTER BOX

Batteries for starter box.Select
according to the starter box
used. Be sure to fully charge
before using.

12

Outer Head

Crankcase

Mounting Lugs

Exhaust

Cover Plate

Carburetor Type 21M

Crankshaft

BASIC ENGINE PARTS

Crankshaft Ball Bearing (Front)

13

Install the exhaust seal
ring supplied.

Exhaust
Seal Ring

Glowplug

Installing the glow plug.
Insert RP7 plug supplied
into heat-sinkhead care­fully, making sure that it is
not cross-threaded before
tightening firmly.
(All the O.S. T-Type plugs
including the RP7 are not
supplied with a washer.)

INSTALLATION OF THE STANDARD ACCESSORIES

About the Head Gasket

The engine is installed with a 0.1mm thick and
a 0.2mm thick gasket for 25% nitro fuel when it
leaves the factory. Also, a 0.2mm thick gasket
is supplied with the engine as standard. Adjust
the total thickness according to atmospheric
temperature, humidity and glowplug used.

8.5mm

Installing the
carburetor reducer

Supplied with the engine.

Standard with the carburetor when it leaves the
factory.

9mm

Insert the taper collet on the crankshaft, taking
care not to push the crankshaft back so that it
contacts the coverplate face.

INSTALLATION OF THE TAPER COLLET

Taper Collet

Cover Plate

Replace the reducer ac­cording to the coursecon­ditions.

14

GLOWPLUG

The role of the glowplug

Glowplug life

Particularly in the case of very high performance
engines,

glowplugs must be regarded as expendable
items. 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.
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.

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

When to replace the glowplug

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.

Since the compatibility of the glowplug
and fuel may have a marked effect on
performance and reliability, it is suggested
to use the O.S. RP7 plug when it is
necessary to replace. Carefully install
plug finger-tight, before final tightening
with the correct size plug wrench.

15

INSTALLATION OF THE CARBURETOR

As delivered, the engine has its carburetor lightly
installed in the intake boss. Secure it as follows.

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

1.

2.

Rotate the retainer nut
gently until it stops.

Tighten a further
120-180

Rotate the retainer screw gently until it
stops, then tighten a further 120-180 .
Do not overtighten the screw as this will
damage the thermo insulator.

Note
Be careful not to damage the O rings when
removing the carburetor retainer from the
engine.
First, remove the retainer Retaining screw,
then pull out each part. Do not push the
part in or damage the O rings.

Retaining Screw

"O" Ring

"O" Ring

16

ENGINE INSTALLATION

Make sure that the vehicle's engine mounting
surfaces are level and in the same plane. Poor
installation may cause distortion of the
crankcase, bearings, etc., resulting in erratic
running and loss of performance.
The recommended screws for securing the
engine are 3mm or 4-40 steel Allen hexagon
socket type.
If existing holes in the engine mount do not align
perfectly with engine mounting lugs, enlarge
them slightly with a needle-file so that screws are
in alignment with the mounting holes.
Also, make sure the engine does not interfere
with chassis, etc.

Chamfer inside edges of bearers.

Do not allow bottom
of crankcase to
touch chassis.

17

CARBURETOR CONTROLS 21M

The Needle-Valve(Adjusted at the factory):

The Mixture Control Valve:

Four adjustable controls are provided on
this carburetor.

For adjusting the mixture strength when the
throttle is fully open.

For changing the mixture strength at mid
speed and acceleration. (Do not rotate the
screw more chan one turn.)

The Throttle Stop Screw
(Adjusted at the factory):

For setting the minimum idle speed:

For adjusting the mixture strength at part­throttle and idle speed, to obtain steady
idling and smooth acceleration to mid speed.

The Metering Needle:

NOTE: Readjustment may be necessary,
occasionally to allow for changes in fuel
formula, gear ratio or clutch engagement point.

Metering Needle

Throttle Stop
Screw

Mixture Control Valve

Needle Valve

Thermo Insulator

Carburetor Reducer

Ball Link

Dust Cover

18

STARTING THE ENGINE & RUNNING-IN ('Breaking-in)

PRESSURIZED FUEL SYSTEM

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Before starting the engine, always
check the tightness of all the screws
and nuts especially those of joint and
movable parts such as throttle arm.
Missing retightening the loose screws
and nuts often causes the parts break­age that is capable of harming you.

Never run your vehicle without installing the
air cleaner. Dust and dirt that may otherwise
be drawn into the engine will rapidly shorten
its life.

The somewhat violent changes of vehicle

attitude that occur in off-road running,

combined with the fact that, in buggy type

cars, the fuel tank is often located some

distance from the carburetor, means that the

fuel 'head' at the carburetor can vary and

upset running.Therefore,it is recommended

that a muffler pressurized fuel feed system be

used.

Running- in is a procedure for an engine to
come close to actual running conditions
(fuel, r.p.m., engine temperature, etc.).

Excessively rich running and prolonged
low speed running should be avoided.
Prolonged low speed running and low
temperature running may result in the oil in
the fuel becoming gelled and the
piston/liner becoming stuck together.

RUNNING-IN ('Breaking-in)

19

The following procedure is suitable when a
fuel containing 25% nitro-methane is used.

Fill the tank completely with fuel.

Temporarily remove the glowplug to check
that it glows bright red when energized.

Glow Plug Igniter

Pliers

Element glows when energized.

Replace the plug when the
element does not glow or is
burnt out.

Turn the needle-valve clock­wise until it stops. This is the
fully closed position.
Do not force it to turn further.

Needle Valve

Open

Close (clockwise)

approx 0.5mm

The carburetor is set at the factory as shown
at the right. Start the engine as it is.

The needle-valve is set approx. 3 turns
opened from the fully closed position.

Throttle is set approx. 0.5mm open.

Approx. 0.5mm open
factory setting with the
reducer removed

Metering needle and mixture control valve
are set at basic position. (Refer to P25.)

20

Turn the engine with starter box to draw fuel
into the engine.

Fuel

Deliver fuel into the carburetor.

Fuel tank side

Now connect glowplug battery lead to heat
the plug filament and start the engine.

Switch on the transmitter and make sure that
each linkage moves correctly.

approx 1mm

Set the throttle opening a little wider that the
factory setting by adjusting the Throttle Stop
Screw.

When the engines does not start or stops
right after started, try the followings.

When the engine star ts, warm it up by
repeatedly increasing the rpm to medium
speed and back again to a fast idle with the
mixture set very rich, the glowplug
connected, and the driving wheels clear of
the ground. The rich mixture will provide
adequate lubrrication and cooling indicated
by profuse exhaust smoke.

Set the needle-valve approx. 2.5 turns open
from the fully closed position.

Do not force the needlevalve to turn beyond
a lightly closed position.

21

It is vitally important to set
the throttle at the correct
position before starting the
engine. If the engine is
allowed to run with the throttle
too far open under ''no load'' conditions (i.e.
with the driving wheels not in contact with

the
ground) it will rapidly over-heat and may be
seriously damaged.

Attention:

throttle trigger

Run the car on the track until one tank of fuel
has been consumed, then close the Needle­Valve 10-15˚ and run the car for 1 to 2 full tanks
of fuel.
Repeat this procedure until approx. 2 liters of
fuel have been consumed, during which time
the throttle may be opened for brief bursts of
increased power.
If the engine stops at medium speeds, close
the Mixture Screw 45˚.

Next, disconnect the glowplug battery and try
running the car on the track.
If the engine stalls, open the throttle
fractionally, but try to keep the engine running
as rich as possible: if it stops because of
being excessively over-rich, close the Needle­Valve 30˚ and try again.

22

Needle

The position of the needle-valve
when starting the engine.

Close the needle-valve approx.
15˚ after running the vehicle for
1 to 2 full tanks of fuel.
Repeat this procedure until
approx. 2 liters of fuel have
been consumed.

Note:
In the event of any major working parts
(e.g. piston/cylinder liner assembly) being
replaced or the fuel being changed,
especially to high nitro fuel, the complete
running-in should be repeated.

Warning!
Do not touch rotating parts, engine and si­lencer when stopping the engine as they
become very hot, and contact with them
may result in a serious burn.

To stop the engine, close the throttle to idle
speed and shut it off completely with the trim
lever on the transmitter then cut off the fuel
supply by pinching the fuel delivery tube to
the carburetor.

Fuel

How to stop the engine

23

FINAL ADJUSTMENT

Throttle
Stop Screw

Needle Valve

Metering
Needle

Open

Close

Close

Open

Needle Valve

Metering Needle

More fuel

Less fuel More fuel Less fuel

Run the vehicle (with throttle fully open) over
the longest available straight course, in order
to observe the model's speed. Next return
the car to the starting point, close the Needle­Valve 10-15˚ and repeat the run, taking note
of the improvement in performance.

Continue with further run s, gradually
reducing the Needle-Valve setting and
aiming to achieve the highest straight-line
speed. Remember, however, that, if the
Needle-Valve is shut down too far, the
engine will overheat and, accompanied by
visibly diminished exhaust smoke, the model
will lose speed. At this point, throttle down
immediately, stop the vehicle and reopen the
Needle-Valve 30˚.

Final adjustment should be carried out only after
the running-in has been completed.

24

Warning!

Mixture adjustments (whether via the
Metering Needle, or the Needle-Valve)
cannot be made accurately under 'no-load'
conditions, which, in any case, are not
advised, since such operation carries the
risk of seriously damaging the engine
through over-revving and overheating.

With the engine running, close the throttle
and allow it to idle for about five seconds,
then reopen the throttle fully. If, at this point,
the engine puffs out an excessive amount of
smoke and the vehicle does not accelerate
smoothly and rapidly, it is probable that the
idle mixture is too rich.

Carry out adjustments patiently, under actual
running conditions, until the engine responds
quickly and positively to the throttle control.

In this case, turn the Metering Needle
clockwise 30-45˚. If, on the other hand, the
engine tends to speed up momentarily and
then cut out abruptly when the throttle is
opened, the idle mixture is too lean. Correct
this by turning the Metering Needle
counter-clockwise 30-45˚.

With the optimum mixture control position,
light smoke is visible during high speed
running,and the engine rpm increases
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 the needle-valve and
metering needle slightly on the rich side of
the best rpm setting, as a safety measure.

25

Mixture Control Valve

Carburetor Body

Slide Valve

Carburetor Body

Metering Needle

Rotate the Metering
Needle until its slotted
head is extruded by

0.5mm the ball link
body. This is the
standard position.

Ball Link

First rotate the Mixture
Control Valve until its
slotted head is flush with
the carburetor body.
This is the standard
position.

In the co ur se of making carburetor
adjustments, it is just possible that the
Metering Needle and the Mixture Control
Valve may be inadvertently screwed in or out
too far and thereby moved beyond its
effective adjustment range. The basic
positions can be found by rotating the
Metering Needle until its slotted head is flush
with the ball link body.

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.

Finally, beyond the nominal break-in period,
a slight readjustment toward a leaner needle
setting ma y be requir ed to maintain
maximum performance.

REALIGNMENT OF METERING NEEDLE AND
MIXTURE CONTROL VALVE

26

CARE AND MAINTENANCE

1.

2.

3.

The minute particles of foreign matter, that
are present in any fuel may, by accumulating
and partially obstructing fuel flow, cause
engine performance to become erratic and
unreliable. O.S. 'Super-Filters' (large and
small) are available, as optional extras, to
deal with this problem. One of these filters
installed to the pickup 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 carburetor.

Do not forget to clean the filters regularly to
remove dirt and lint that accumulate on the
filter screens. Also, clean the carburetor itself
occasionally.

At the end of each operating session, drain out
any fuel that may remain in the fuel tank.
Afterwards,energize the glow-plug and try to
restart the engine, to burn off any fuel that may
remain inside the engine. Repeat this
procedure until the engine fails to fire. Do this
while the engine is still warm.

4.

Then, inject some after-run oil into the
engine, and rotate the engine 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-rings
inside the carburetor to deteriorate. These
procedures will reduce the risks of starting
difficulties or corrosion after a period of
storage.

27

Installing Dust Caps

When storing the engine, install the cap on
the exhaust port, carburetor, etc. to prevent
dust from entering the engine.

Dirt and dust may lodge in
marked places.

CHECKING THE ENGINE

Engine will not develop normal performance
after long time running due to wearing of parts.
It is suggested to replace necessary parts when
the following symptoms are detected.

Engine sound changes and easily overheats.

Power has dropped extremely.

Idling is unstable and/or engine tends to stop
at idling.

In most cases, ball bearings, cylinder & piston
assembly, connecting rod and/or crankcase have
become worn out or abnormal. Check the
parts carefully and replace them if necessary.

5.

Finally, when cleaning the exterior of the
engine, use methanol or a household
cleaning agent. Do not use gasoline,
kerosene, or any petroleum based chemical
which can damage silicone fuel tubing.

Crankshaft of this engine is filled with
silicone. Do not use light oil nor
kerosene, etc. for washing, or the
silicone will swell. Use alcohol or fuel for
washing.

Note:

28

TROUBLE SHOOTING

Symptom

Cause

Corrective action

Engine fails to fire.

Fuel tank is empty.
Fuel not reaching the engine.

Fill the tank with fuel and repeat
Priming procedure.

Glowplug element is burnt out.
Glowplug battery discharged

Replace glowplug.
Recharge or replace the battery.

Clogged fuel filter
Air cleaner and silencer inside is dirty.

Clean or replace fuel filter.

Replace cleaner element and clean inside silencer.

Over priming Remove glowplug and pump out excess fuel.

Fuel tubing is disconnected.

Connect fuel tubing securely.

Fuel tubing is kinked, split or has a hole.

Check the tubing carefully and replace if necessary.

Incorrect servo linkage Connect correctly after setting servo at neutral.

Reverse rotating direction of starter box.

Mare sure it rotates counter clockwise seen
from crankshaft side.

29

Symptom

Cause

Corrective action

Engine fires intermittently but does not run.

Insufficient fuel in the tank. Fill the tank with fuel.

Deteriorated glowplug

Replace glowplug.

Clogged fuel filter
Air cleaner and silencer inside is dirty.

Clean or replace fuel filter.
Replace cleaner element and clean inside silencer.

Engine overheated

Wait until engine is cool.

Incorrect clutch release

Adjust the tension of clutch spring.

Starting battery disconnected too soon.

Do not disconnect plug battery and wait until
r.p.m. becomes stable.

Vibration causing air bubbles in fuel.

Install "O" rings to the tank screws to
prevent bubbles.

30

Symptom

Cause

Corrective action

Symptom

Cause

Corrective action

Unstable idle

Unsuitable glowplug

Use suggested glowplug in the instructions.

Unsuitable fuel

Do not use extremely high nitro or low oil content fuel.

Extremely light flywheel

Add heavier flywheel.

Silencer is disconnected or has play

Install silencer securely.

Not reaching expected peak r.p.m.

Insufficient warming up or running-in.

Set the needle only after warming up.
Complete running-in.

Silencer or manifold is not securely connected
or disconnected.

Replace seal ring.
Check the connections and secure them.

Fuel tubing from tank is split or broken.

Replace the tubing.

31

Symptom

Cause

Corrective action

Symptom

Cause

Corrective action

Poor response

Deteriorated glowplug Replace glowplug.

Incorrect carburetor settings

Readjust low r.p.m. range with metering
needle and mixture control valve.

Incorrect setting of transmitter Exponential function.

Check the transmitter setting.

Poor r.p.m. drop

Throttle position open too far.

Close metering needle to adequate position
to lower idle r.p.m.

Carburetor not fully seated

Install carburetor securely.

Incorrect linkage

Make sure the throttle servo linkage does not
bind and is connected correctly.

Metering needle closed too far.

Open the metering meedle a little.

32

1

3

2

4

5

6

7

10

11

12

13

14

15

C.M2.6x18

C.M2.6x7

C.M3x18

8

9

16

17

ENGINE EXPLODED VIEW

Type of screw

C…Cap Screw

＊

CAP SCREW SETS

(

10pcs./sets

)

Code No.

Size Pcs. used in an engine

Carburetor Retainer Retaining Screw (1pc.)

79871055

M2.6x18

33

ENGINE PARTS LIST

The specifications are subject to alteration for improvement without notice.

Outer Head

Inner Head

Head Gasket Set (0.2mm)

Head Gasket Set (0.1mm)

Cylinder & Piston Assembly

Piston Pin

Piston Pin Retainer (2pcs.)

Connecting Rod

Carburetor Complete (Type 21M)

Carburetor Retainer Assembly

Crankshaft Ball Bearing (Front)

Crankcase

Crankshaft Ball Bearing (Rear)

Crankshaft

Cover Gasket

Cover Plate

Screw Set

Glow Plug RP7

Head Gasket Set (0.2mm)

Exhaust Seal Ring (2pcs.)

Carburetor Reducer 9mm (Blue) W/"O"Ring

"O" Ring

Flywheel No.1E Collet

Dust Cap Set ( 3mm,16mm, 18mm)



Description

Code No.

No.

123456789

10111213141516

17

22014000

22014100

22014160

22014170

22013000

22016000

21817000

23755020

22082000

23981740

23731000

22011000

23730020

22012000

23764020

22417000

23763010

71642070

22014160

22826140

71533010

22615000

71801100

22884250

34

S.M3x3

1

1-1

1-2

2

2-1

3

4

8

9

10

5

8-1

7

3-1

11

5-1

4-1

6

10-1

5-1

12

CARBURETOR EXPLODED VIEW

Type of screw

S...Set Screw

35

The specifications are subject to alteration for improvement without notice.

CARBURETOR PARTS LIST

1
1-1
1-2

2
2-1

3
3-1

4
4-1

5
5-1

6

7

8
8-1

9

10

10-1

11
12

22082600
46066319
22781800
22082970
46066319
22082940
22082950
22848160
27881820
71533385
22615000
22082100
22082200
22082340
27881820
23981520
23781400
26381501
23781110
29015019

Mixture Control Valve Assembly
"O" Ring (L) (2pcs.)
"O" Ring (S) (2pcs.)
Needle Assembly
"O" Ring (2pcs.)
Needle Holder Assembly
No.15 Universal Nipple Assembly
Throttle Stop Screw
"O" Ring (S) (2pcs.)
Carburetor Reducer (8.5mm Purple)
"O" Ring (1pc.)
Carburetor Body (w/Thermo Insulator)
Slide Valve
Metering Needle Assembly
"O" Ring (S) (2pcs.)
Dust Cover
Ball Link No.3
Set Screw
Thermo Insulator
Carburetor Rubber Gasket



Code No.

No.

Description

36

(71641800)

O.S. GENUINE PARTS & ACCESSORIES

(71642060)

RP6

(71642070)

RP7

O.S. Glow Plug

RP8

(72412000)

(72412100)

(72412200)

(71521000)

(73300305)

(73301612)

Dust Cap Set

3mm

16mm

(5pcs.)

(3pcs.)

The specifications are subject to alteration for improvement without notice.

Super Air Cleaner 202 Assembly

202 Cleaner Body

202 Filter Element (4pcs.)

Long Socket Wrench With Plug Grip

On-road Type

(73301812)

18mm

(3pcs.)

37

4- 3.3

31.6
45

45

37

21

29.5

15.6

28.5

87.7

44 21.6

UNF1/4-28

■

■

■

■

■

■

3.49 cc (0.213 cu.in.)

16.27 mm (0.640 in.)

16.8 mm (0.661 in.)
4,000-45,000 r.p.m.

2.7 hp / 33,000 r.p.m.
348 g (12.32 oz.)

Displacement
Bore 
Stroke 
Practical R.P.M. 
Power output 
Weight

SPECIFICATIONS

THREE VIEW DRAWING

Dimensions (mm)

38

MEMO

C

Copyright 2009 by O.S.Engines Mfg. Co., Ltd. All rights reserved. Printed in Japan.

60092260 091002

TE L. [phone]

FAX. [phone]

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

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