Saito FG-21 User Manual

15”x 8”～16”ｘ6”

s

4-Ø4.2

66

50

E.C.

50

Outside dimension

1733

66

52

60

63.5 25 13.7

The 4-Stroke engine provides 4 individual piston
movements as illustrated below. The “Stroke”
means the piston movement from the Top Dead
Center to the Bottom Dead Center. In the 4-Stroke
engine, one cycle of operation in change of gas

Mechanism of 4-Stroke Engines

state inside the cylinder and valve movement are

102.5

71.8

E.C.

26.8 25.4

47.3

4-Ø4.2

34

40

22

completed at every 4 strokes of piston that is every
2 revolutions of the crankshaft. Formally the
engine is called the 4-stroke one-cycle engine.

Fig.1

43.2

M8x1.25

40 76 26.2

179

31.5

1. Propeller
Depending on the airframe, please adopt the standard size in the data and use a reliable product which is generally on the market.
(Carbon made prop is recommended)
Since a large-diameter prop is used, please maintain sufficient balance. Since an imbalanced prop is vibratory and dangerous with
lowered performance, please maintain balance with a balancer. Moreover, a cracked prop is dangerous. Please be sure to check any
time and replace it with a new one if it’s cracked.

*Prop and fuel consumption
If the load is large (the diameter & pitch of the prop is large) for the engine characteristics, the air-fuel mixture should be rich. Thus
the main needle has to be opened. That is, even if the revolution is low, the fuel consumption is high. Conversely, when the load is
small and the revolution is high, the fuel consumption is lowered because the main needle can be closed.
In order to decrease the fuel consumption and prolong the engine life, a propeller should be used whose revolution is maximized when
the throttle-valve is fully opened, while using an airframe which enables all flights with about 90% of the output of the propeller. In
this case, the throttle valve will be further throttled during horizontal flight. On the contrary, an airframe which can only deliver
performance in fully open condition will suffer worsening fuel consumption and life.

2. Fuel
The fuel is mixture of commercial regular gasoline and reliable oil for 2-stroke. (In addition, unleaded high-octane gasoline is not
necessarily required for our engine.) [Example of oil]

・ POWER LUBE (KLOTZ ORIGINAL TECHNIPLATE)
・ KLOTZ GS RC model LUBE
・ CASTROL POWER1 TTS Racing, etc.

For the mixture ratio, please be sure to use “gasoline : oil = 20 : 1” or richer by volume ratio. Any damage caused by the fuel used, in
which the oil ratio is lower than 20:1 ratio, is not warranted.
Since gasoline is a dangerous material, be careful of its storage, use, and transport enough. (The evaporative emission and exhaust
smoke of gasoline have a harmful effect on a human body. Also, if gasoline is leaked, there is danger of fire etc.) Please note that we
takes no responsibility for accidents, health damages, etc which occur during storage, use and transport of gasoline.

3. Fuel Filter and fuel pump
Since commercial gasoline has many impurities, please be sure to use a reliable filter for
the admission port of the gasoline fuel pump (Fig.2) or the filter with weight in the fuel
tank as the following picture shows.
Without using a filter, the performance of the carburetor is not delivered, resulting in
failures.

4. Fuel tank and piping
For the capacity (about 200cc-250cc), refer to the data and select the best of commercial
product. Please be sure to use a filter with weight. To avoid entrain any impurities to the
carb, piping with “Fuel feeding pipe” and “Air inhalation pipe” (Fig.3) is recommended.

*Please be sure to use “gasoline-proof” products for the tank lid rubber, piping, and

tubing. Some of the products for glow fuel can’t be used for gasoline. Please check
carefully if there’re any clack of the piping, tubing, connection, and tank. All of the
connection part should be bound by thin Nylon strap or wire to avoid fuel leakage or air
induction to the fuel line. (If there are any leakages, the performance of the engine
decreases dramatically.)

*The tank should be placed within the range of 200mm from the engine center to the tank

center. When performing an acrobat with a large change in fuel level or that requiring an
excessive movement of throttle, the tank must be placed at a position close to the engine
as much as possible.

*When provide “Air inhalation pipe” as Fig.3, arranging the tube above the fuel level

(Fig.4) is the effective way of fuel leakage prevention.

-2-

Filter with weight (tank is not included)

Gasoline-proof
Pump

Filter with weight

Fig.2

Gasoline-proof tube

Fire wall

Fuel feeding pipe

to Carb nipple

Air inhalation
pipe

Rubber cap for
gasoline-resistant

Fuel tank
(200-250cc in capacity)

Fuel level

to Outside of
the fuselage

Fig.4

above

Fuel level

Air inhalation
pipe

Fig.3

Engine center

Gasoline-proof tube

Within 200mm (close as possible)

Filter with weight

Center of fuel tank

5. Ignition system (Fig.5)
The ignition system is designed to match our 4-stroke engines with automatic advancing system.
However this ignition system is designed to be an anti-noise product, please isolate it completely from the receiver, servo, and battery to
avoid a radio-interference trouble. Moreover, it is desirable to utilize a noise filter (line filter). Especially, each switch (for Ignition and
for Receiver) should be isolated and set far from each ones.
The function of each cord;
(1) Plug cord (meshed high tension cord)

The tip of the plug cap is designed exclusively for SAITO SP-1 Plug. When you put on the plug cap, insert it to the plug until the
clip fits the groove on the plug (Fig.6; then you will hear clicky sound) to avoid coming off during flight. And then pull the plug
cap to make sure that it won’t come off.
When you put off, pinch the clip and pull up the plug cap (Fig.7).

(2) Sensor cord (black /red/white cord)

Connect with the cord from the sensor attached to the engine.

(3) Battery cord (black/red cord)

Please use the fully charged battery that has adequate spec. (6-8V, more than 1000mA is recommended.). Between the battery and
main body, make sure to set an ignition switch whose capacity is higher than 3A.

Noise check (required)

Caution: A gasoline engine generates a noise which has an adverse effect on RC adjustment unlike a glow engine. Please be sure to carry out a
noise check each time while the engine is running before the flight. Since a noise which occurs during flight may lead to a large-scale accident,
please carry out a noise check without fail.
As a simple method, after starting engine you can check by removing the antenna of the transmitter and operate it about 50m away from the
airplane. If there is no malfunction, it is normal. Moreover, it is preferable to obtain advices from an expert of gasoline units.

Plug cap

Plug cord

Main unit

Switch (not included)
Capacity: more than 3A

Battery cord

Sensor

Fig.5

Sensor cord

Battery
Voltage: 6-8V
Capacity: 1,000mA or higher

*Sensor position and Power / Starting easiness;
The ignition sensor can be moved to CW (advance the spark timing) or CCW (delay the timing) as Fig.8
shows.
At the factory default the sensor is fixed on the center (neutral) position. The reason is related to the
methods of engine starting.

・With an electric starter-You can start wherever the sensor is fixed.

So you can set the sensor as the rpm reaches maximum speed.

・By hand flip (Manual start)-Starting easiness depends on the sensor position.

The factory default is set as you can start by hand flip and also get highest rpm in that range as possible.
If you prefer easiness of hand starting, move the sensor to CCW direction to delay the spark timing. But
then the maximum rpm will slightly decline.
If you prefer power (highest rpm), move the sensor to CW direction. But then you can't start by hand
flip but only with starter.
In addition by the feature of the ignition system, it heats up with engine running. When you restart the
engine by hand flip, you should open the throttle valve slightly while it's hot. And it's better to enlarge
the choke without wetting the plug.
For safety we recommend to use an electric starter.

-3-

Fig.6

Fig.7

CW

Fig.8

View from front

Advance

Spark timing

Neutral Position

Prop rotation

Delay

Spark timing

Hand start

(CCW)

CCW

easy area