A D J U S T M E N T O F T H E C A R B U R E T O R
9
8
S T A R T I N G T H E E N G I N E
contacts. Clean any possible excess
fuel (an indication of engine flooding)
and screw it in again. Further starting
should only be done with the throttle at
idle position. If the plug is dry, probably
not enough fuel has been drawn into
the carburetor. If that is the case, check
the fuel feed and then return to the
instructions in paragraph A.
Note:
We strongly urge the use of a
tachometer to check rpm readings when
breaking in the engine.
After starting and warming the engine
for 30 to 45 seconds adjust as follows:
For initial break-in: do not exceed
4,000 rpm for the first 10 minutes of
operation. This allows all the parts to
mate properly with good lubrication.
Step I. Move the throttle to 2/3
high throttle position quickly (fast
acceleration). Repeat three times. If the
engine accelerates smoothly go to Step
III. If acceleration is not smooth, go to
Step II.
Step II. Faulty acceleration and a
tendency to quit is usually attributable
to a poor fuel mixture in the medium
rpm range. Stop the engine and recheck
the fuel feed. The fuel line must not be
pinched or broken. Restart the engine
and test acceleration again. If the
problem persists adjust the carburetor.
Open the low-speed needle by 5 minutes
and retest. If acceleration is smooth,
open the needle by another 3 to 5
minutes. This should be done because
the needle was previously set too lean.
If the engine continues to not accelerate
properly, open the low-speed needle by
10 minutes. If the engine’s operation
does not improve, shut it off and check
the basic setting, restart the engine
and test the acceleration. If the engine
continues to not accelerate properly, the
defect is likely to lie somewhere other
than an adjustment. If the engine runs
correctly, go to Step III.
Step III. If the engine accelerates
correctly, set it at idle speed and
accelerate to full speed. Repeat twice
more. If the engine functions correctly,
go to Step IV. If it cuts out, open the
low-speed needle valve by 5 to 10
minutes more. If the engine does not
respond to acceleration fast enough,
keep closing the low-speed needle until
the engine starts to cut out in response to
throttle opening. At that point, re-open
the low-speed needle by 5 to 10 minutes.
Step IV. If the engine reacts correctly,
set it at full speed. If the revolutions do
not drop, the engine has been adjusted
successfully. If the revolutions seem to
drop, open the high-speed needle by
about 5 to 10 minutes.
CAUTION:
The engine must be
stopped while you adjust the carburetor
in order to prevent injury by the
propeller. Subsequent runs may be made
while slightly leaning out the mixture
with each tank full of fuel. Forty
minutes is considered sufficient time for
normal breakin prior to the first flight.
The use of a tachometer is encouraged
for setting the high-speed needle valve
prior to flight. The peak rpm should be
obtained and then reduced by 200 to 300
rpm. Over-revving of a 4-stroke engine
can cause internal damage to the engine.
Adjustment of
the Carburetor
The low-speed needle valve is set at the
factory so that idle rpm may be between
1,800 and 2,100 rpm.
In principle, a carburetor is adjusted
by first achieving highest rpm with
the high-speed needle valve and then
performing idling (low speed rpms)
with the throttle valve and the low-
speed needle valve. (Unless peak rpm
is achieved, idling adjustment will be
difficult to adjust and will not be stable.)
• After filling the tank, start the engine
and move the throttle to the fully
open position.
• Turn the main needle valve screw
clockwise (refer to Figure 5, page
7) with the carburetor adjustment bar
(provided in the accessories package)
or a small screw driver, and adjust to
achieve peak rpm. Use a tachometer
to verify rpm.
CAUTION:
Over-closing the main
needle valve is very dangerous because
it may cause knocking and preignition.
It may also cause the propeller nut
to loosen. Immediately turn the main
needle counterclockwise to richen up
the setting.
• Next, close the throttle valve until
the engine operates stably and with
an idle rpm of around 1,700 rpm. Do
this by adjusting the low-speed needle
valve with the carburetor adjustment
bar (or small screwdriver) and
manipulating the throttle valve via
the throttle stick on the transmitter.
• After reaching the stable 1,700 rpm,
slowly open the throttle fully. If the
rpms become slow or go up suddenly,
adjust carefully until the changes
are smooth from idle to peak rpm, by
adjusting the low-speed needle valve.
• After the previous steps have been
accomplished, repeat the process
from idle to high rpm quickly. If the
rpms do not reach peak, but stutter as
the throttle moves from low to high,
re-tune the main needle valve and
perform the process from idling to
peak quickly.
• Repeat the process until the response
is a smooth transition from idle to
peak rpm.
Factory settings for the main and low-
speed needle valves are as follows.
• Main needle valve: Turn needle valve
all the way clockwise and then back
14387 SAI FG_20andFG_36 Manual.indd 8-9
12/16/08 2:09:13 PM
