14
F G - 1 4 B / F G - 2 0 S E T T I N G T H E N E E D L E V A L V E S
F G - 1 4 B / F G 2 0 S E T T I N G T H E N E E D L E V A L V E S
15
Setting the Needle
Valves in the Gas 4
Stroke Engines
Use a Tachometer
When setting any 4 stroke engine it is critical
that a tachometer is used in setting the needle
valves. It is near impossible to set them
properly by ear. A good quality tachometer will
go a long way towards improving your usage
of these engines and make the experience
even more enjoyable. Make the investment.
Set the High-Speed needle First
A general starting point for the high-speed
needle on the FG-14B carb is 1 turn 30 mins.
and the FG-20 carb is 1 turn 40mins.
1. Start the engine, and using your
tachometer gradually lean the high-
speed needle valve until the engine
reaches its peak rpm.
a. This will take some patience
because it will take a few seconds
after making a 1 click needle
change to register an increase.
b. As you hit the perfect peak setting
you will notice that there will be no
rpm change.
c. Now go further in the lean direction
until you notice an rpm decrease. It
is only once you have experienced
the rpm decrease can you be sure
that you have actually reached the
peak setting.
2. Once you are sure that you are on the
lean side richen (open) the high-speed
needle back to the peak rpm.
3. Open the high-speed needle 2 clicks rich
from your confirmed peak and leave it
there. You will likely notice a small rpm
difference on your tachometer, but you
will not likely be able to hear this drop
in rpm.
Set the Low-Speed needle
The baseline settings for all Saito carbs are
taken from the point where the adjustment
end of the low-speed needle valve is flush
with the throttle control arm. This in itself
lends a degree of inaccuracy to our starting
point because each of us can determine ‘flush’
at a slightly different position. Because of the
design of the carb it is not possible to give a
setting from ‘closed’. Specific starting settings
for the FG-14B and the FG-20 are different to
please consult the appropriate section of the
manual.
1. With the engine running, and the high-
speed needle valve set as above, adjust
your throttle setting to achieve the
desired idle speed.
note:
The more your prop weighs the lower
your achievable idle speed will be.
2. Check the transition of the engine from
low-speed to high-speed. To do this
let the engine idle for a period of 10
seconds and then rapidly move the
throttle from low to wide open. There
are one of three things that will happen:
a. The engine will respond immediately
and the transition will be very
smooth to wide open throttle.
b. The engine will stumble and
gradually increase rpms to wide
open throttle. In this case the idle
needle setting is too rich. Make a
very small adjustment to lean the
needle (clockwise rotation) and try
again. Continue to do this until you
achieve an immediate response
from the engine.
c. The engine will abruptly quit when
the throttle is opened. This indicates
a too-lean low-speed setting. Open
the low-speed needle valve a small
amount (counterclockwise) and try
again. Continue to do this until you
achieve an immediate response
from the engine.
recheck the
High-Speed needle Valve Setting
You need to go back and recheck the high-
speed needle valve setting again as described
above after adjusting the low-speed setting.
Because of the design of the needle assembly
adjusting the low-speed needle actually
affects the size of the fuel aperture and can
affect the high-speed needle setting.
Enjoy Your new Engine
Once you have set your needle valves the final
tuning will occur in the air. Listen carefully to
your engine while it is running.
If rpm starts to drop a couple of minutes
•
into the flight, or when you climb the
airplane, your high-speed needle is a bit
lean. Land as soon as you can and richen
the high-speed needle settings a couple of
clicks and take off again.
If during flight your engine has good
•
power but occasionally sounds like it
‘misses’ this is a good indication that you
are running the engine too rich. The next
time you land lean the engine out one
click at a time until you are happy with the
performance in the air.