Carburetor Mixture Screw Adjustments
The
most
common
cause
of
poor carburetion
is
unsatis-
factory adjustment
of
the
idle
or
main
mixture
adjust-
ment screws. Significant variation from the correct set-
tings may result in serious engine trouble. An overly rich
mixture not only wastes fuel, but can increase engine
wear by washing the lubricant from the cylinder walls
and diluting the crankcase
oil.
An overly lean mixture
results in a
loss
of
power, flat spots
in
acceleration,
and
a greater tendency
to
burn valves and spark plugs.
Mixture screw adjustment should be checked with
every engine tune-up and whenever a carburetion prob-
lem is suspected. Before adjusting, be sure the ignition
system
is
working properly and thegovernor is correctly
set. The limiter cap on the main mixture screw should
not be removed unless the carburetor is totally out of
adjustment or has been overhauled. With the limiter cap
removed, use the mixture settings in Table 6-2 for preli-
minary adjustments. Turn the mixture screws in until
lightly seated, then turn out the specified number of
turns.
*
L
TABLE
6-2.
CARBURETOR ADJUSTMENT SPECIFICATIONS
MIXTURE SETTING FLOAT
LEVEL
9/16
i
1/16
in.
I
(14
*
*
Inm’
I
I
I
I
I
T
H
R
0
l-r
L
E
STOP
SCREW
ADJUSTMENT
Forcing the mixture adjustment
-1
screws fight will damage fhe needle
and seat. Turn in
on/y
mil
right
fension can be
felt.
AWARNING
Contact with moving parts can cause
severe personal injury. Keep
clothing, jewelry, hands, and fingers clear while
adjusting the governor.
A
hot generator set can cause severe
k!@@&l
burns. Always allow the generator
set
to
cool before touching any components or remov-
ing any parts.
Start the engine and allow it
to
run for about
10
minutes.
The location of the adjustment screws
is
shown in Fig-
ure 6-9. Use the following procedure
to
adjust:
1.
2.
3.
4.
5.
6.
7.
Stop the set and connect a voltmeter, frequency
meter, and load bank
to
the generator output leads.
Start the generator set and apply a full load. Verify
that the frequency is within
60.5
f
1
hertz
(50.0
f
1
hz on
50
hertz units) and adjust the governor speed
adjustment screw
if
necessary
to
obtain required
frequency.
Turn the main adjustment screw inward until volt-
age or frequency drop and then outward until volt-
age or frequency drop again. Locate the point
where the voltage and frequency are highest. From
this setting turn the main adjustment screw
out
an
additional
1
/4
turn.
Remove the load and verify that frequency is within
62.5
-1:
0.5
hertz
(52.0
5
0.5
hz on
50
hertz units).
Adjust governor speed adjustment nut
if
necessary
to
obtain required frequency.
When the engine is warm, and the set is running at
no load, turn the speed adjustment screw (Figure
6-6)
so
that the throttle lever on the carburetor is
resting against the throttle stop screw. Adjust the
stop screw
to
obtain a setting of
55
?
1
hertz
(45.0
-t
1
hz on
50
hertz units).
Turn the idle adjustment screw inward until voltage
and frequency drop and engine begins
to
run rough
or starts hunting. Back out idle adjustment screw as
required for smoothest operation without hunting.
Recheck setting in step
5.
Release the governor linkage and observe the sta-
bility
of
the set. Set the voltage and frequency and
adjust the sensitivity
of
the governor as specified in
Governorin this section. Add and remove a full load
several times
to
make certain the set does not bog
down or hunt.
-
FS-1759
FIGURE
6-9.
MIXTURE SCREW ADJUSTMENT
6-1
3
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