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Saito FG-21 Instructions Manual Page 4

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6. Spark plug
SAITO SP-1 spark plug is the standard equipment. Dimensions are as follows;
Hexagon width: 8mm
Reach (with a washer): 5.5mm
For replacement, please specify "SAITO SP-1".
Since our four cycle engine uses a mixed gasoline, please decide the numbers of flights by yourself and clean the spark plug. Please
replace, when it is degraded. (Consider the plug as consumable).
7. Carburetor
A carburetor with a pump developed exclusively for our small-size four cycle gasoline engine is mounted, instead of using muffler
Since the carburetor with a pump introduces the air from the air hole shown in the next figure, set it 2mm or more apart from the firewall
or drill a hole on the firewall.
When adjusting the carburetor, refer to Fig.9
Main needle: To adjust the speed at the time of full open of the throttle valve.
Slow needle: To adjust the speed from the idling to the middle speed.
Turning each needle in clockwise direction, the fuel will become leaner and the rotation speed will increase. Turning it in counterclock-
wise direction, the fuel will become richer and the rotation speed will decrease.
Note: The carburetor for the gasoline engine is the assembly of very strict and delicate parts. So please make sure to use filtered gasoline.
Moreover, DO NOT disassemble by yourself. If there're any troubles regarding carb, please consult the shop from which you bought the engine.
8. Engine mounting, muffler attachment, and breather waste disposal
Make sure to use our standard engine mount attached. Otherwise, any other mount might cause troubles
regarding heat or vibration.
Make the firewall robust enough because this part has to endure vibration and torque caused by prop
It is preferable to apply some adhesives (such as screw lock) on the tip of M4 cap screw to avoid loose-
ness when you install the engine.
To ensure that cooling wind passes through the engine and muffler, the cowling should be devised. Also
make the air flow outlet larger than the inlet. Building some baffles inside the cowling appropriately will
enhance the cooling efficiency. Insufficient cooling may cause engine trouble such as overheat or muffler
The muffler should be securely tightened with screw lock in the procedure to tighten up a double nut
using two spanners.(Adhesives, such as a screw lock agent, are effective against looseness and leakage.)
For breather treatment, there is also a method in which the aluminum pipe, etc. are fixed at the muffler
outlet to diffuse the hot air together with exhaust gas into the air. (Breather may function by simply
ejecting the tube from the engine)
And one of the effective way of disposal is, to set a brief filter made by a small case and a tissue inside as
the figure shows.
9. Preparation before engine start (assuming break-in)
(1) Please mount the engine on a robust and parallelized test bench or on the fuselage. (In either case,
the engine should be fixed and immobile.)
(2) Check whether the throttle valve can be fully closed and opened certainly.
(3) Check whether each wiring of the ignition system is connected certainly.
(4) Use 300-400cc tank for the test bench.
(5) For piping, only connecting the carburetor with the tank is needed.
(6) For fuel, prepare a mixed gasoline with volume ratio of "gasoline : oil" = "20 : 1"
(7) Prepare a well balanced 16"x 6" carbon-made prop (Bolly or Mejzlik).
*Prop attachment position
Since our 4-stroke gasoline engine can be manually started in forward direction (CCW from the front view) of the rotation, fix
the prop in the position which facilitates vigorous clanking.
(8) When starting with an electric starter, also attach a spinner. (This way of start is recommended for safety.)
Note: Please tighten up the prop regularly at least once in ten flights. Especially for a wooden prop, it tends to compressed so that
the nuts are rather easy to be loosen so please confirm carefully that the nuts are tightened adequately.
(9) Unlike 2-stroke engines it is difficult to judge clearly the peak condition on 4-stroke engines. Prepare a tachometer to prevent
over-throttling or overheat.
Screw size: UNEF 1/4-32
Spark-gap: 0.4-0.5mm
Cool air
Muffler outlet
Alminum pipe
Breather nipple
To outside


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