-5-
(2) Open the main needle 2 turns from that state and use the throttle stick to fully open the throttle valve. If rich air-fuel mixture
canʼt be obtained, open the main needle additionally. Then continue running for more than 1 tank. During this initial
operation, contact of each part inside the engine will be matched. So make the fuel mixture rich as much as the engine
doesnʼt stop. Do not care about running smoothness at this step.
(3) Refill the tank and run the engine with the main needle to achieve peak and less speed (richer) alternately about 5 times.
And then maintain the peak condition long gradually. When it gets stable, then operate the throttle stick to vary slow speed
to high speed several times to check the response. After that run it for 1 tank keeping high speed.
(4) When it comes to run smoothly at peak, break-in on the ground is completed. Then perform tappet adjusting referring to
Chapter 14 and adjust the carburetor referring to Chapter 13. After that, fly it for about 20 times in rich condition to finish
break-in in the air.
Also after break-in, please run the engine in rich condition as long as it doesnʼt affect to the flight.
13. Adjustment of carburetor
Since a gas-engine has narrow range of air-fuel ratio, adjustment of the needles is stricter than a glow-engine. And both
needles are interfered slightly from each other so confirm the balance of peak and response after adjustment.
In principle, the carburetor should first achieve peak by adjusting the main needle. Then performing idling with the throttle
valve and the slow needle. (Unless the peak is certainly achieved, idle adjustment will be difficult and not stabilized.)
*The slow needle is set as to keep around 1,500~1,800rpm at idling at factory default.
(1) After filling up the fuel tank, start the engine as described in Chapter 11 and run it for 1 minutes in rich condition. Then fully
open the throttle valve with the throttle stick.
(2) By turning the main needle with the adjustment bar observing tachometer and exhaust sound, achieve peak carefully.
(3) Next, close the throttle valve until the engine runs stably with an idling rotation around 1,500rpm by adjusting the slow
needle with the adjustment bar carefully. (During flight, itʼs rather stable with slightly high adjusted at idling. )
*The best richness of the air-fuel mixture at slow speed is depend on the flight style. Generally, Scale flight requires stability in
low speed so slightly lean condition is preferable. On the other hand Acrobatic flight requires quick response from low
through high, so slightly rich condition is preferable.
(4)Once the idling is set, get the throttle valve fully opened gradually. If the revolution becomes slow or goes up suddenly,
adjust the slow needle carefully until rpm raises linearly from idling to peak by fine-tuning.
(5)After adjustment of (4) is completed, perform the process from idling to peak quickly. If revolution gets delayed to achieve
peak even if the throttle valve is fully opened, fine-tune the main needle and perform the same process. Repeat this
fine-tune and response check carefully until the response improves.
A tip for carb adjustment is to set the slow needle slightly lean as long as the engine doesnʼt stop when open the throttle
valve quickly from low to high.
For the main needle, rich condition as far as it doesnʼt affect to the flight is a knack to increase the engine life.
The best tune varies depending on many factors such as weather, quality of the oil, prop, and so on.
During your flights, please perform fine-tune so that low-middle-high speed matches best with the airplane.
Note： During early stage of flights, take the height high enough to land safely in case the engine stop in the air suddenly. It
will reduce the risk of crash or landing accident.
Caution：Too much throttling the main needle is very dangerous because it might cause knocking and the prop nut might be came
off. Once you notice abnormal vibration or sound during throttling the main needle, just return to open the needle immidiately.
14. Normal operation, maintenance, and additional information
(1) After completing ground break-in or operating the engine for 1 hour, adjust tappet gaps (valve clearances) by following
procedure to compensate initial wearing, while the engine is cold (Fig.10). To perform it first, either cylinder is OK.
(a) Remove the plug and rocker covers from the cylinder.
(b) Turn the prop slowly forward by hand until the rocker arm of intake stops. Further turn the prop to bring the piston to
the TDC (Top Dead Center) of compression stroke.
(c) Use the attached wrench and hexagonal wrench to adjust the gaps indefi-
nitely close to zero within the range compression exists. If the gap is lower
than 0, the valve has to be opened at all phases so the compression
doesnʼt occur (then, loosen the screw to reset).
After adjustment, put on the spark plug and turn the prop forward to check
if the compression is enough.
(d) On checking the gap, securely tighten (but not excessively) the lock nut.
(e) Do the same adjustment for the other cylinder.
* In the case of the engines for vehicle, small gap is given to tappets to absorb
valve elongation. However for SAITO engines, gap becomes larger during operations due to thermal expansion of the cylinder
(made of aluminum). Therefore set the gap indefinitely close to zero when the engine is cold.
(2) Just after start up the engine, perform warm up running in rich condition for about 1 minute, and just before stop run it at
idling for 1 minute to cool down as well.
(3) When stop the engine after the final flight of the day, be sure to stop by cutting the fuel to remove fuel from the carburetor.
And remove the fuel from the tank and reserve it with special care.
(4) Since the fuel contains more than 5% of oil, sometimes the exhaust valve gets dull by carbon or sludge especially in cold
atmosphere. Then turn off the ignition switch and rotate the prop by electric starter. After dilute the oil content by this way,
remove the fuel from inside the carb and the engine. It helps the valve to move smoothly.
Or, remove the rocker cover and applying some anti-rust spray to the exhaust valve is effective as well.
Tappet adjustment
Fig.10
Must not be inserted
(over gap)
Limit gauge
(0.1mm)
Close to "0" with no limit
Note: Occasionally check tappet gap by those procedure. When the attached gauge (limit gauge, t=0.1mm) comes to be inserted, gap has
been enlarged beyond the allowable limit. Make an adjustment to lessen the gap. Tappet gap is one of the most important factors in the
maintenance of 4-stroke engines. Operating the engine with the tappet gap enlarged excessively will cause poor performance or troubles.
