O.S. Engines 91HZ 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 model, radio control equipment, etc., are
accessible for checking at the same time.

1

2-5

6-7

8-9

10-12

17-21

25-29

35

42-43

44-45

46

30-34

22

36-37

38-41

13-16

23-24

47

48

CONTENTS

SAFETY INSTRUCTIONS AND
WARNINGS ABOUT YOUR O.S. ENGINE

NOTES ON INSTALLING,
COOLING-FAN AND CLUTCH

NOTES WHEN APPLYING AN ELECTRIC STARTER,
INSTALLATION OF THROTTLE SERVO

NOTES ON HEATING THE GLOW PLUG
INTRODUCTION, ENGINE PARTS NAME 

BEFORE STARTING,
INSTALLATION OF THE ENGINE

INSTALLATION OF THE STANDARD ACCESSORIES

GLOWPLUGS

CARBURETOR CONTROLS

STARTING, RUNNING-IN("Breakingin")

ADJUSTMENT

ADJUSTMENT CHART

CARE AND MAINTENANCE

TROUBLE SHOOTING

ENGINE EXPLODED VIEW & PARTS LIST

CARBURETOR EXPLODED VIEW & PARTS LIST

O.S. GENUINE PARTS & ACCESSORIES

THREE VIEW DRAWING

MEMO

!


!


2

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 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

!


WARNINGS

•

•

•

•

•

Never touch, or allow any
object to come into contact
with, the rotating parts.

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 flam e,
excessive heat, sources of
sparks, or anything else which
might ignite it. Do not smoke
or allow anyone else to smoke,
near to it.

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.

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

!


4

NOTES

•

•

•

•

•

This engine was d es ig ned for model
helicopters. 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.

Install an effective silencer (muffler). Frequent
close exposure to a noisy exhaust (especially
in the case of the more powerful high-speed
engines) may eventually impair your hearing
and such noise is also likel y t o c ause
annoyance to others over a wide area.

Check the linkage to the throttle arm before
each flight.

Avoid sudden high r.p.m. immediately after the
engine is started, as the clutch will engage and
you may be struck by the rotor.

•

•

After starting the engine, carry out any needle­valve readjustments after stopping the rotor by
closing the throttle to the lowest r.p.m..
Stop the engine before attempting to make
other adjustments to the carburetor.

Use an electric starter. The wearing of safety
glasses is also strongly recommended.
Press the rotor head down securely.

Take care that the glow plug clip or battery
leads do not come into contact with rotating
parts.

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.

•

•

5

!


NOTES

•

•

•

Take care that loose clothing (ties, shirt sleeves,
scarves etc.) do not come into contact with the
rotor. Do not carry loose objects (such as pen­cils, screwdrivers, etc.) in a shirt pocket from
where they could fall through the rotor disc.

For their safety, keep all onlookers (especially
small children) well back (at least 20 feet or 6
metres) 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.
Hold the rotor securely and keep well clear of
spectators.

Warning! lmmediately after a glowplug-ignition
engine has been run and is still warm,
conditions sometimes exist whereby it is just
possible for the engine to restart when turned
over WITHOUT the glowplug battery being
reconnected. Remember this if you wish to
avoid the risk of accidents.

6

Notes on installing cooling fan and clutch

Do not use a tool which locks piston
when installing a cooling-fan and
clutch, or top of the piston may be
damaged. Also, do not insert a
screw driver or the similar into the
exhaust port.

It is recommended to use Crankshaft
Clamp 91 (Code No.71530510) available
as an optional tool.

7

Notes on installing cooling fan and clutch

Do not grip the engine mounting
beams with a vise, or the crankcase
will be distorted which will result in
engine breaking.

Vise

Beam Mount

8

NOTES WHEN APPLYING AN ELECTRIC STARTER

Because of this initial tightness, a
standard electric starter may have
difficulty in rotating the engine when
cold, before it has been adequately
run-in. In this case, use a high-torque
type 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 pumped out fuel from
getting into your eyes.

9

F

J

J

F

28
34

27

33

A

B

90°

90

°

A=B

Linking the throttle servo to the carburetor
Link the throttle servo to the carburetor using the throttle lever supplied.
Throttle control rod A and B should be equal length. Set the linkage so that
the servo output lever and throttle lever are parallel when the throttle stick on
the transmitter is at middle position. Installing hole intervals on the F lever and
on the J lever are different. Decide the lever to use according to the servo used.
Be sure to cut off another lever to avoid any interference.

10

Note on heating the glow plug

The heatsink head on the engine is
treated with an anodized finish which
does not conduct current. Therefore,
when heating a glow plug, connect
one lead to the glow plug and the
other to the head or cover plate
retaining screw.

Example

11

Standard accessories

Glow Plug No.8

Needle Adjusting Screw (M2.6x5 2pcs.)

Needle Control Arm

Carburetor Complete 61E

Note:

As delivered, the carburetor is not
installed on the engine.

Carburetor Rubber Gasket

Head Gasket

(0.2mm)

This is a high performance engine
expressly designed for 90 size RC model
helicopters.
It performs perfectly from stable hovering
to dynamic aerobatic maneuver, which is
required for F3C competition. 61E
carburetor has three adjustable controls
which enables independent adjustment at
idling, hovering and high speed.
Needle control arm is supplied with the
engine as standard.
The needle can be tuned by the transmitter
in flight or with a fully enclosed engine.
The cover plate has a cell to accept a
sensor designed to install in the cover plate
from the Futaba GY-701 Governor.

INTRODUCTION

12

Heatsink Head

Carburetor
Typr 61E

Crankshaft

Propeller nut

Crankcase

Glowplug

Beam Mount

Cover Plate

High Speed
Needle Valve

Fuel Inlet

Mixture Control Valve

Throttle Lever

Idle Mixture Control Screw

Mixture Control
Valve Stopper

Thrust Washer

Carburetor Rubber Gasket

Medium Speed
Needle Valve

Crankcase
Heatsink

Thermo Insulater

ENGINE PARTS NAME

13

Items necessary for starting

Tools, accessories, etc.The following items are
necessary for operating the engine.

Glow Plug

O.S. No.8 is supplied with the engine.

Battery leads

Glowplug battery

The power source for heating the glowplug may be
either a large heavy-duty 1.5volt dry cell, Ni-cd battery
or glowplug Igniter.

1.5 volt dry cell

These are used to conduct current
from the batter y 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.

Battery leads

glowplug Igniter

Make sure glowplug element
glows bright red inside room
or shadow.

Battery leads

In case of 1.5volt dry cell

12V Battery

Starter

Electric starter and starter
battery

An electric starter is recom­mended for starting.

Hexagon starting shaft

This shaft mounte d on an
electric starting motor is driven
into the shaft cup to turn the
engine.

BEFORE STARTING

14

Select, by practical tests, the most suitable fuel from among
the best quality fuels available in your country for helicopter
use. For the best throttle response, a fuel containing 10% to
30% 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 deterriorate and may
adversely affect running qualities. If in
doubt compare to a fuel known to be good.

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.

Reminder!

Fuel

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.

Alternatively, one of the purpose-made
manual or electric fuel pumps may be
used to transfer fuel directly from your
fuel container to the fuel tank.

Manual

Electric

Install a filter to the outlet tube of your
refueling container to prevent entry of
foreign matter into fuel tank. O.S. ‘Super
Filters’ (large and small) are available as
optional extras.

O.S. Super Filter (Fuel Can Filter)

It is recommended to install a good in­line filter between the fuel tank and
carburetor to prevent entry of foreign
matter from getting into the carburetor.

Fuel Filter

Heatproof silicone tubing of approx.
5mm o.d. and 2.5mm i.d. is required
for the connection between the fuel
tank and engine.

Fuel Pump

Silicone Fuel Line

15

TOOLS

Screwdriver

Necessary for engine installation.

1.5mm, 2mm, 2.5mm, 3mm

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

Phillips Screwdriver

No.1, No.2, etc.

Socket Drivers

5mm, 5.5mm, 7mm

Hex Drivers

8mm

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

End Wrenches

8mm, 13mm, 14mm, etc.

Needle Nose Pliers

Long Socket Wrench With Plug Grip

16

The under-surfaces of all O.S. engine beam
mounting lugs are precision machined flat and
exactyly parallel to the engine's horizontal axis. It is
essential that the engine mounts in the model are
also accurately made and aligned. If they are not,
they will cause stress and distortion within the engine
itself, probably resulting in loss of performance and
internal damage.
The recommended screws for securing the engine to
the engine mounts in the model are 4mm or 4-40
steel Allen type. It is also advisable to use lock
washers or LOCTITE to prevent nuts from loosening.

Front view

CORRECT

Side view

Top surfaces are in the same plane.

Re-align the surfaces as necessary

INCORRECT

Top surfaces are not
in the same plane.

Top surfaces are not in the
same plane.

Engine does not rest firmly.

Make sure that on ly the unde r­surfac es of the e ngine’ s mounting
lugs are in contact with the engine
mount.

INSTALLATION OF THE ENGINE

17

INSTALLING THE GLOWPLUG

Install washer on glowplug
and insert carefully into
Heatsink-head, making sure
that it is not cross-threaded
before tightening firmly.

Glow plug

Washer

ABOUT THE HEAD GASKET

The knurled heads of the two needle valves (High­Speed and Medium Speed) ar e provided with
dia gon al sl ots f or us e with a screwdr iver.
Alternatively, formore positive location via an Allen
hexagonal key, these heads also have M2.6 internal
threads, into which M2.6x5mm Allen cap-head screw
may be installed. To avoid risk of damage to the fuel
passages when tightening these screws, remove the
needle valves from the carburetor and use 'Loctite'
thread-lock compound to secure the screw.

HEX KEY NEEDLE ADJUSTMENT

Needle Adjusting screw

The engine is installed with a 0.1mm thick head
gasket at the factory. When a 15% nitro fuel is used,
run the engine as it is. When a 30% nitro fuel is used,
replace with a 0.2mm thick gasket supplied or add

0.2mm thick gasket for easier tuning.

INSTALLATION OF THE STANDARD ACCESSORIES

18

INSTALLATION OF THE CARBURETOR

1.

2.

Retainer screw

Carburetor Rubber
Gasket

0.2mm gap

Carburetor Rubber
Gasket

Inser t th e ca rb uretor rubb er gas ke t on the
carburetor body securely.
Then, insert the carburetor in the crankcase.

Note: In case it is hard to insert the carburetor in
the crankcase, apply oil on the Thurmo Insulater.
Do not force it, or damage to the Thermo Insulater
and/or crankcase can occur.

Rotate the retainer screw gently until it stops, then
tighten a further 90-120 degrees.
Do not over-tighten the screw as this will damage
the Thermo Insulater.

3.

Loosen carburetor retainer screw a little.

Retainer screw

19

1.

2.

The Needle Control Arm enables the pilot to make
the necessary needle adjustment by means of one of
the auxiliary levers on his transmitter while the
helicopter is in flight. Then the following useful
corrections can be made.

Needle can be adjusted to optimum setting while the
helicopter is in flight.

When the needle is set too rich or too lean during a
performance at a competition, the needle can be
adjusted via transmitter in flight.

When the r.p.m. increase as the fuel tank changes
from full to almost empty, the situation can be
corrected by opening the needle.

Note:
In order to use this Needle Control Arm , an
additional servo and a linkage rod are required.

Features:

ABOUT THE NEEDLE CONTROL ARM

Cap Screw

Ratchet Spring

Needle Control Arm

High Speed Needle Valve

It is not always necessary to install
the needle control arm

How to install

Remove the high speed needle taking care not to
damage it’s point.

Install the control arm on the needle with a M2.6x5
bolt supplied.

20

1.

2.

3.

Connect the Needle control Arm lever and servo
horn with the linkage rod. Set the linkage so that
the Needle control Arm lever and servo horn
makes right angle at the center of servo stroke.

3.

approx.
14-16mm

The throw angle of the servo horn should not be
more than 45 degrees both right and left. Use a
hole approx.15mm from the center of the servo
horn.

Servo

Servo Horn

Linkage Rod

(commercially available)

Equal distance

Close the high speed needle slowly to fully closed
position. Then, open the high speed needle two
turns and remember it’s position.

Switch on the transmitter and then receiver. Check
all the movements. Confirm moving direction of the
servo vs. transmitter stick travel volume direction.

Move the transmitter stick travel volume fully in the
direction which opens the high speed needle.
Connect the linkage rod, and install the control arm
on the high speed needle.

ADJUSTMENT

45 degrees

45 degrees

21

5.

6.

4.

WARNING:

Lean running affects the engine performance very
much. Always try to run the engine at slightly rich
setting.

Close the high speed needle by moving the
transmitter stick travel while actually flying the
model.
It is suggested for safety to carry out this
adjustment after landing the model specially when
you are not accustomed with it’s operation.

If the engine runs rich even if the transmitter stick
travel is moved fully in the direction the high speed
needle closes, stop the engine and remove the
control arm from the high speed needle.
Remember the opening of the high speed needle at
this time.

Repeat procedure 3.

22

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 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
No.8, No.7 and No.10 (Former A5) .
Carefully install plug finger-tight, before
final tightening with the correct size plug
wrench.

23

With a fixed-wing model, power failure is rarely a
serious threat to the safety of the aircraft since it can
usually glide down to a safe landing. In a helicopter,
on the other hand, it is vitally imporant that the engine
keeps running and that there is a quick and reliable
response to the throttle in order to ensure safe ascent
and descent of the model.

The High-Speed (Main) Needle Valve

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

The Idle Mixture Control Screw

This provides the means of manually adjusting the
mixture control valve. By setting the Mixture Control
Screw for the best idling performance, the mixture
control valve automatically ensures that fuel is
accurately metered to maintain the correct mixture
strength as the throttle is opened.

Three adjustable mixture controls are incorporated in the
Type 61E. They are as follows.

A

B

The Medium Speed Needle Valve

This is an extra control that can be brought into
play, if necessary, after adjusting A and B above. It
provides the means of fine-tuning mixture strength
over that all-important part of a helicopter's throttle
range where the model is flying in, or near, the
hovering mode.

C

Idle MIxture Control Screw

High Speed Needle Valve
(Main Needle)

Medium Speed
Needle Valve

As the idle mixture control screw is installed with
LOCTITE, it may initialy feel stiff, and it is suggested
to use a slightly oversized screwdriver. The screw can
be turned only 90 degrees either way. Do not force to
turn further, or it may break or cause trouble.

NOTE

90 degrees

90 degrees

CARBURETOR CONTROLS

24

BASIC POSITION OF MIXTURE CONTROL SCREW
(Mixture Control Valve)

Thick

Mixture Control Valve

MIxture Control Screw

Lean

As delive re d, t he M ixture Control Screw is
positioned at approximately the center as shown in
the sketch. Mixture gets lean when the Mixtur e
Cont rol Screw is turned right, w hile mixt ure gets
rich when the Mixture Control Screw is turned left.
With a model helic opt er, adjustments vary with
combined various factors such a s cli ma ti c
conditions, fuel, muffler, main rot or, weight of the
model, gear ratio, etc. Therefore th e Mixture
Control Screw position varies with each model and
set- up, and it is normal if the Mixture Control Screw
position is off the center.

89 degrees

When the triangle mark on the carburetor rotor meets
the far right mark, the throttle is fully closed. When
the triangle mark meets the top mark, the throttle is
fully open. The range is 89 degrees. You may use
the other three marks as the reference marking of
throttle opening to your preference when hovering.

WARNING!
Never try to check the triangle mark position
while the engine is running and rotor is rotating,
or you may be hit by rotating rotor which results
in serious injury. Stop the engine and rotor
before checking the triangle mark position.

Carburetor Rotor

Carburetor Body

Fully closed
position

Fully opened position

As shown i n the sket ch, the carb ureto r has
graduation marks.

GRADUATIONS ON THE CARBURETOR BODY

25

!


Be sure to use an electric starter to start
the engine.

Fill the fuel tank with fuel. When filled, prevent the
fuel from flowing into the carburetor with a
commercially available fuel stopper, etc. Release
the stopper before starting the engine.

1.

2.

Starting procedure is as follows:

WARNING
When checking the plug element hold the plug
with tools, such as pliers, etc.
Do not hold near your face or the fuel remaining
in the filament may burn you.

Glow Plug Igniter

Pliers

Element glows when energized.

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

Make sure that plug element glows red, and install
the plug in the cylinder head.

Never fail to check the tightness of screws
and nuts, especially engine mounting and
moving parts (e.g. throttle lever).

Be sure to use a muffler pressurized fuel feed.
Use the same fuel as you intend to employ for
actual operation of your model.

STARTING

26

Open

1.

2.

Opening and closing of the Needle-Valve

Turn the needle clockwise to close the needle­valve, and turn the needle counter-clockwise to
open the needle-valve as shown in the sketch.

High Speed needle-valve:

two turns open from the fully closed position.
(Note: If a different muffler is used, this setting
may require readjustment)

Idle Mixture Control Screw:

at basic position when the engine leaves the
factory.

two turns open from the fully closed position.

Medium Speed needle-valve:

Close

4.

Checking the rotating direction of the starter

Make sure that the starter rotates
to the direction shown in the
sketch. If the direction is reverse,
reverse the leads on battery.

3.

Preparation of the starter

Install the starting shaft to the
starter securely.
Improper installation will allow the
shaf t to swing creat ing a
dangerous situation.

High Speed
needle-valve

Idle Mixture Control Screw:

Medium Speed needle-valve:

27

5.

Inserting the starter shaft

Insert the starting shaft into the
shaft cup securely.

6.

Priming

Without energizing the glowplug, open the throttle
a little from the idle position. Turn the engine over
using the starter until the fuel is seen to reach the
carburetor.

Stopping the engine

Fully pull down the throttle trim on the transmitter.

Starting

Connect the battery to the glowplug and start the
engine by applying the starter. When started, switch
off the starter and withdraw the starting shaft after
making sure the rotation of the starter shaft stops.

Preparation of starting

7.

8.

9.

Hold the rotor head by hand so that rotor cannot
rotate when the engine is Started. Also, steady the
model with a foot on the landing gear skid.

Make sure that the transmitter
throttle stick is at the fully closed
position and the throttle trim at
center position, and make sure
tha t idle-u p swi tch on the
transmitter is off.

28

In case the engine does not stop.

Hold the rotor head, and pinch the fuel line to stop the
fuel supply. If it still does not stop, pull off the fuel line
from the carburetor.
It is necessary to readjust the throttle linkage so that
the carburetor rotor is fully closed when the throttle
stick and throttle trim on the transmitter are fully
pulled Down.

NOTE:

If the throttle response is poor or the engine
stops due to a temporarily over-rich mixture im­mediately after the engine is started, pinch the
fuel line for one or two seconds until the engine
r.p.m. increase and the engine runs steadily.

Reminder!

Never touch, or allow any object to
come into contact with, the rotating
rotor.

29

All internal-combustion engines benefit, to some
degree, from extra care when they are run for the first
few times known as running-in or breaking-in.

This allows the working parts to mate together under
load at operating temperature.

However, because O.S. engines are made with the
aid of the finest modern precision machinely and from
the best and most suitable materrials, only a very
short and simple running-in procedure is required and
can be carried out with the engine installed in the
model.

For the first few flights with a new engine i.e. while
the engine is being run-in set the needle-valve for a
slightly rich mixture not excessively rich as this may
result in poor throttle response and cause the engine
to stop.

About one half turn open from the nomal setting will
usually suffice.

RUNNING-IN ("Breaking-in")

30

Please observe the following before beginning to
make any adjustment.

High-Speed Needle Valve. Turn this approximately
30 degrees (3 to 4 clicks) at a time, when making
initial adjustments; then in steps of approximately
15 degrees (1 to 2 clicks) when making final
adjustments.

Medium-Speed Needle Valve. Turn approximately
30 degrees (3 to 4 clicks) at a time.

Idle Mixture Control Screw. Turn approximately 5
degrees at a time. It turns approximately 90
degrees both sides from the center. Turn left to
enrich the idle mixture and turn right to lean the idle
mixture.

The general course of adjustment procedure is
shown in the ADJUSTING CHART and is correct
for a fuel containing 20% lubricant and 15-30%
nitromethane.

Bear in mind that fuels containing relatively large
percentages of power-boosting nitromethane operate
at richer mixture settings than are needed for mild
fuels and will, therefore, require the High-Speed
Needle Valve to be readjusted accordingly. The type
and percentage of lubricant used is also a factor
here, as noted later in these instructions.

This carburetor is not equipped with a throttle
stop screw. Instead, idle speed is adjusted by
means of the throttle trim lever on the trans­mitter.

ADJUSTMENT

31

As a safety measure, first check the transmitter
controls, including the throttle stick and trim lever
positions, and hold the main rotor securely before
starting the engine.

Warm the engine by allowing it to idle for about 30
seconds. If the engine stops, advance the throttle
trim lever slightly to increase the idle rpm.
Then open the throttle sufficiently to 'float' the
model above the ground. lf, at this time, the
engine is slow to pick up and produces an excess
of exhaust smoke, the mixture is too rich.
Corr ect this c ondition by turni ng the Mixture
Control Screw clockwise 5 degrees. lf the mixture
is extremely 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.

ADJUSTMENT PROCEDURE

1.

This condition may also be initiated by an
excessively prolonged warming-up period. lf, on
the other hand, the mixture is too Iean, this wiIl be
indicated by a marked lack of exhaust smoke and
a tendency for the engine to cut out when the
throttle is opened. ln this case, turn the Mixture
Control Screw counter-clockwise 5 degrees to
enrich the mixture.

32

Having provisionally set the idle mixture, the next
step is to adjust the mixture for hovering flight.
Hover the model and actuate the throttle to observe
response over the medium speed range. lf the
engine smokes excessiveIy and throttle response is
poor, the mixture is too rich ; in which case, land the
model and turn the High-Speed Needle Valve
clockwise. Do not close the High-Speed NeedIe
Val ve more than the recomm ended initia l
adjustment (3 to 4 clicks) at a time, keeping it a little
on the rich side at this stage. DO NOT touch the
Medium Speed Needle Valve.

lf, on the other hand, hovering is not stable and
response to the throttIe is over-sensitive, or if the
engine tends to overheat, this indicates that the
mixture is too lean and should be corrected by
turning the High-Speed Needle Valve counter­clockwise.

2.

After about 10 seconds of idling, open the throttle to
'float' the model. lf the transition is smooth, the idle
mixture is O.K. If the symptoms of either rich or Iean
running are

observed, readjust the Idle Mixture

Control Screw accordingly.

NOTE: With this carburetor, neither the Idle
Mixture Control Screw adjustment, nor the
Medium Speed Needle Valve adjustment will have
any effect on mixture strength when the throttle is
fully (or almost fully) open.

Throttle Opening

Fully Closed

1/3

2/3 Fully Open

Fuel Flow

Maximum

Minimum

Adjustment range of Idle Mixture
Control Screw

Adjustment range of Medium
Speed Needle Valve

Needle Valve too
far open

Needle Valve too
far closed

High Speed Needle
Valve Setting varies
according to the curve.

When satisfactory hovering flight has been achieved,
land the modeI again and re-check the engine's idle
qualities.

33

Now re-check hovering performance It may be
found that (with the High-Speed Needle Valve
now set for optimum full-throttle performance)
hovering will reveal symptoms of slightly lean
running at medium speeds. DO NOT touch the
High-Speed Needle Valve.

Now adjust the High-Speed Needle Valve to
achieve the best performance when the model is
flying at full throttle. lf, at full throttle, acceleration
is poor, the exhaust unduly smoky and the model
fails to reach expected straight line speed, the
mixture is too rich and the High-Speed Needle
Valve setting will need to be reduced.
lf, however, after smo othly acc eIerating to
satisfactory high-speed straight and level flight,
power is lost when the model is puIled up into a
climb, the mixture is too lean. ln this case, land the
model immediately and readjust thw High-Speed
Needle Valve to a richer setting.

3.

4.

Having now found the optimum setting for the
High-Speed Needle Valve, re-check the engine's
idle performance, fine tuning the Idle Mi xtur e
Control Screw, if necessary, to perfect the idle.

5.

It is at this point that the Medium Speed Needle
Valve, previously set two turns open, may be
brought into operation. Open the Medium Speed
Needle Valve 30 degrees, or 3-4 clicks, then fine
tune until the optimum hovering performance is
obtained. If on the other hand, hovering reveals
rich running, close the Medium Speed Needle
Valve gradually until the optimum hovering
performance is obtained.

34

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. 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 carburetor and, furthermore, that
this filter is frequently cleaned to remove foreign
matter that accumulates on the filter screen. Finally,
occasionally remove the needle-valve holder from the
carburetor as shown in Photo and extract any
remaining foreign matter that may have lodged in the
location shown in Photo, right.

Remove this with
an 8mm wrench

Dirt and fbrous matter
mostly accumulate here

SUBSEQUENT READJUSTMENTS

Once the engine has been run-in and the carburetor
controls properly set up, it should be unnecessary to
alter the mixture settings, except to make minor
changes to the Main (High-Speed) Needle Valve
occasionally, to take account of differences in climatic
condisitions.
However, as previously mentioned, the use of a
different fuel, particularly one containing more, or
less, nitromethane and / or a different type or
proportion of lubricating oil, is likely to call for some
modification to the High-Speed Needle-Valve
adjustment.
As a safety measure, it is advisable to increase the
High-Speed Needle Valve setting by an extra half­turn counter-clockwise, prior to establishing the 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
Needle-Valve setting.
The use of a different glowplug, or changes to the
main rotor and its pitch angles may also require
compensating carburetor readjustments.

35

ADJUSTING CHART

High Speed Needle Valve - 2 turns open from fully closed position.

Medium Speed Needle Valve - 2 turns open from fully closed position.

Start the engine

Warm up the engine

Observe the mixture condition while "floating" the model

Turn the Idle Mixture

Control Screw counter-

clockwise 5 degrees

Idling OK

Turn the Idle Mixture

Control Screw

clockwise 5 degrees

Lean mixture

Rich mixture

Observe the hovering mixture condition

Open the High Speed

Needle Valve

(Turn counter-clockwise)

Hovering OK

Lean mixture

Rich mixture

Close the High Speed

Needle Valve

(Turn clockwise)

Land the model

Idle for approx: 10 seconds, then reopen throttle to

observe transition ("Float" the model)

Idling OK

Lean mixture

Rich mixture

High Speed Flight

Lean mixture

Rich mixture

High Speed Flight OK

Fine tuning of hovering mixture

Open the Medium

Speed Needle Valve

Hovering OK

Adjustment completed

Open the High Speed

Needle Valve

(Turn counter-clockwise)

Close the High Speed

Needle Valve

(Turn clockwise)

Fine tuning of idling mixture

Lean mixture Rich mixture

Idling OK

Lean mixture Rich mixture

Close the Medium

Speed Needle Valve

Turn the Idle Mixture

Control Screw

clockwise 5 degrees

Turn the Idle Mixture

Control Screw

clockwise 5 degrees

Turn the Idle Mixture

Control Screw counter-

clockwise 5 degrees

Turn the Idle Mixture

Control Screw counter-

clockwise 5 degrees

36

CARE AND MAINTENANCE

Please pay attention to the matters
described below to ensure that your engine
serves you well in regard to performance,
reliability and long life.

As previously mentioned, it is vitally important
to avoid operating the engine in conditions
where dust, disturbed by the propeller, may
be deposited on the engine and enter its
working parts.

Remember to keep your fuel container
closed to prevent foreign matter from
contaminating the fuel.

Install a fuel filter to prevent foreign matter in
the fuel container from entering the fuel tank.
O.S. Super Filters (L) and (S) are available
as optional extras.

Install an in-line fuel filter between the tank
and carburetor to prevent foreign matter in
the tank from entering the carburetor.

If these precautions are neglected, restriction
of fuel flow may cause the engine to cut out,
or the fuel/air mixture to become too lean
causing the engine to overheat.

Clean these filters periodically.

The use of modern high-performance alcohol
based model engine fuels, while promoting
cooler running, improved anti-detonation
combustion and increased power, have the
disadvantage of causing corrosion due to the
acid by-products of combustion.
The use of nitromethane in the fuel can also
contribute to the problem.

37

Do not close the needle-valve and mixture
control valve too far as this will cause a lean
setting and over heating of the engine. This
can, in turn, create nitromethane oxide
leading to internal rusting of the engine.
Always adjust the needlevalve slightly on the
rich side of peak rpm.

Do not leave unused fuel in the engine at the
conclusion of a day’s flying. Accepted
practice is to cut off the fuel supply while the
engine is still running at full throttle, then
expel as much fuel residue as possible by
turning the engine over 5-10 seconds with
the electric starter.
Finally, inject some after-run oil through the
glowplug hole and turn the engine over
several times by hand.

When the engine is not to be used for some
months (for example, as between flying
seasons), a worthwhile precaution is to
remove it from the airframe and, after
washing off the exterior with alcohol (not
gasoline nor kerosene), remove carefully the
carburetor with intake pipe, glow plug and all
silicone tubing and put them safely aside.
Then, immerse the engine in a container of
alcohol. Rotate the crankshaft while the
engine is immersed. If foreign matter is
visible in the alcohol, rinse the engine again
in clean alcohol. Finally, shake off and dry
the alcohol ,and inject some after-run oil in
the glowplug hole and rotate the crankshaft
several times by hand. Reinstall the
carburetor with intake pipe and glowplug on
the engine and keep it in a dry place after
putting in a vinyl bag.

38

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. Silencer inside is dirty.

Clean or replace fuel filter.

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 carburetor settings

Return the needle valve
and mixture control valve to basic position.

Incorrect servo linkage

Reconnect linkage after setting servo at neutral.

Reverse rotating direction of electric starter.

Mare sure the engine rotates counter clockwise
seen from crankshaft side.

39

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
Silencer inside is dirty.

Clean or replace fuel filter.
Clean inside silencer.

Engine overheated

Wait until engine has cooled.

Disconnecting plug battery too soon.

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

Air bubbles in fuel

Fit O rings to the tank screws to
prevent bubbles.

40

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 fuel.

Silencer is disconnected or is loose 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.

Check the connections and secure them.

Fuel tubing from tank to is split or broken.

Replace the tubing.

41

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.

Poor r.p.m. drop

Too much throttle opening at idle.

Lower the throttle trim to adequate position
to lower idle r.p.m.

Incorrect carburetor fitting

Fit carburetor securely.

Inaccurate linkage

Recheck the throttle opening against
the pitch angle.

Needle-valve closed too far.

Open needle-valve slightly

42

ENGINE EXPLODED VIEW

Type of screw

C…Cap Screw

＊

79871055

79871140

79871150

M2.6x18

M3x12

M3x15

CAP SCREW SETS

(

10pcs./sets

)

Code No.

Size Pcs. used in an engine

Cylinder Head Retaining Screw (6pcs.)

Cover Plate Retaining Screw (4pcs.)

Retainer Screw (1pc.)

C.M3x15

1

2

3

4

5

6

7

8

9

10

11

12

14

15

16

C.M3x12

17

19

18

13

13-1

C.M2.6x18

43

The specifications are subject to alteration for improvement without notice.

ENGINE PARTS LIST

123456789

101112

13

13-1

1415161718

19



29074000

29061405

29073100

29503400

29073200

26606008

27917000

29505010

29088010

45010002

46120000

26731002

29081720

45566310

29071000

27930000

29072000

29061410

29067001

29077100

71608001

71705100

41621100

29061406

Heatsink Head

Head Gasket

Cylinder Liner

Piston Ring

Piston

Piston Pin

Piston Pin Retainer (2pcs.)

Connecting Rod

Carburetor Complete 61E

Propeller Nut

Thrust Washer

Crankshaft Ball Bearing (Front)

Carburetor Retainer Assembly

"O" Ring

Crankcase

Crankshaft Ball Bearing (Rear)

Crankshaft

Cover Gasket

Cover Plate

Crankcase Heatsink

Glow Plug No.8

Needle Control Arm

Needle Adjusting Screw

Head Gasket (0.2mm)

No.

Description

Code No.

44

CARBURETOR EXPLODED VIEW

Type of screw

C...Cap Screw

4

4-1

4-2

4-3

5

6

7

8

9

9-1

9-2

9-3

9-4

10

11-1

11-2

11-3

11-4

11

13

12

C.M3x8

1

1-1

2

3

C.M2.6x7

79871020

M2.6x7

CAP SCREW SETS

(

10pcs./sets

)

Code No.

Size Pcs. used in an engine

Rotor Guide Washer
Retaining Screw (1pc.)

45

The specifications are subject to alteration for improvement without notice.

CARBURETOR PARTS LIST

No.

Description

Code No.

Throttle Lever Assembly

Throttle Lever Retaining Screw (2pcs.)
Carburetor Rotor
Rotor Guide Washer
Mixture Control Valve Assembly
"O"Ring (L) (2pcs.)
"O"Ring (S) (2pcs.)
"O"Ring (2pcs.)
Rotor Guide Screw
Carburetor Body
Mixture Control Screw
Mixture Control Valve Stopper
Needle Valve Assembly (Main Needle)
Needle Assembly
"O"Ring (2pcs.)
Needle Valve Holder Assembly
Ratchet Spring
Fuel Inlet

Needle Valve Assembly
Needle Assembly
"O"Ring (2pcs.)
Needle Valve Holder Assembly
Ratchet Spring
Thermo Insulater
Carburetor Rubber Gasket
Needle Adjusting Screw (5pcs.)

No.

Description

Code No.

1

1-1

2
3

4
4-1
4-2
4-3

5

6

7

8

9
9-1
9-2
9-3
9-4

10

29085140
22826131
29088210
25881220
29085510
27881810
27881800
27881820
45581820
29088100
27881330
27681340
29085900
29085910
24981837
29085940
26711305
29085950

11
11-1
11-2
11-3
11-4

12

13

27981900
27981910
24981837
27381940
26711305
27984900
27915000
41621100

46

(71531000)

(71531010)

(72403050)

(55500003)

(71530510)

(71521000)

(L)

91

M4

LONG SOCKET WRENCH
WITH PLUG GRIP

SUPER FILTER

LOCK WASHER
(10set)

O.S. GENUINE PARTS & ACCESSORIES

The specifications are subject to alteration for improvement without notice.

GLOWPLUG

CRANKSHAFT CLAMP

NON-BUBBLE
WEIGHT

NON-BUBBLE
WEIGHT

S

(71605100)

No.10 (Former A5)

(71608001)

No.8

(71607100)

No.7

14.95 cc (0.912 cu.in.

)

27.7mm (1.091 in.

)

24.8mm (0.976 in.

)

2,000〜16,000 r.p.m.

3.4 PS / 15,000 r.p.m.
618g (21.82oz.)

47

THREE VIEW DRAWING

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

SPECIFICATIONS

Dimensions(mm)

JAPAN

JAPAN

43
61

25

52

42

42.8

27.4

UNF 5/16-24

88.7

42.5

56.4

12

81.2

36.9

4- 4.2

48

MEMO

C

Copyright 2008 by O.S.Engines Mfg. Co., Ltd. All rights reserved. Printed in Japan.

60092340 121005

TE L. [phone]

FAX. [phone]

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

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