CARBURETORS : STEWART
Ordinarily, a sufficient range of adjustment can be obtained
by means of the screw (V).
In the event, however, that it should be found, upon adjusting
the carburetor, that the mixture cannot be made sufficiently
lean when the screw (V) is turned all the way to the left,
or sufficiently rich when turned all the way to the right,
this can be taken care of by shifting the adjustment arm (K)
relative to the pinion shaft, to which it is clamped.
To make this adjustment, first disconnect the adjustment arm
spring and then loosen the adjustment arm clamp screw (U).
In case the mixture cannot be made lean enough by turning the
screw (V) all the way to the left, the adjustment arm should
be shifted one notch, or serration to the left.
In case the mixture cannot be made sufficiently rich when the
adjustment screw (V) is turned all the way to the right, the
adjustment arm should be shifted one notch to the right.
To prevent the pinion shaft from rotating when the arm is removed,
and thus losing the adjustment entirely, it is desirable to either
remove the cap from the lower part of the gear housing and take
out the small spring beneath the metering pin, or tighten the
packing gland which surrounds the pinion shaft sufficiently so
as to create enough friction to prevent the pinion rack spring
from moving the pinion shaft.
After shifting the adjustment arm, the clamp screw should be
tightened and the spring connected, and the final adjustment
made in the regular manner by means of the adjustment screw (V).
It is well so to locate adjustment arm relative to the pinion
shaft that when the carburetor is finally adjusted for running
conditions the adjustment screw V will be approximately in the
center of its travel, which will permit making the mixture either
leaner or richer to suit seasonal changes.
In case the location of the adjustment arm is completely lost,
this can be restored, so that no difficulty will be encountered
in starting the engine, by the following means: Detach the carburetor
from the engine and then remove the throttle body, or upper part,
by unscrewing the two cap screws. This will expose the metering
valve head.
Then, with the adjustment arm spring disconnected, also the clamp
screw (U) loosened, the pinion shaft should be turned to the
right (using the adjustment arm (K) as a wrench) so that the
metering pin will be forced up into the metering valve, lifting
same from its seat.
Next, turn the pinion shaft in the opposite direction very slowly
until the metering valve just touches its seat.
Measurement should then be taken of the distance between the
end of the gear housing (X) (with the cap removed) and the rack
(T) which carries the metering pin and slides within the gear
housing. This can be done with a narrow scale or depth gauge.
Next turn the pinion shaft to the left, which will force the
metering pin rack down its of an inch. This distance can be measured
with the scale or depth gauge.
Then carefully remove the adjustment arm from the shaft, without
turning same, and replace (again being careful not to turn the
shaft) in such a position that the adjustment arm will come opposite
the point of the adjustment screw when same is turned down approximately
one-half of its total travel.
Next the clamp screw should be tightened and the adjustment arm
spring connected. This will give an approximate adjustment so
that the engine can be easily started, and after bringing up
to normal temperature, the final setting should be made by means
of the screw (V).
Flooding of Carburetor
Flooding or overflowing of the carburetor may result from one
of several causes, such as leaky float or failure of the needle
valve to seat because of dirt or other foreign matter. A leaky
float is easily determined by shaking it near the ear. It should,
of course, contain no fuel.
In case the fuel supply contains foreign matter, this may become
lodged between the point of the needle and its seat, causing
the carburetor to flood. In this connection it is well to remove,
from time to time, the strainer (AA) located at the lower part
of the carburetor, and thoroughly clean it of any dirt or sediment.
Should flooding be due to improper seating of the needle valve,
this can sometimes be corrected by removing the cap from the
center of the float chamber, which will expose the needle valve
stem, and which can then be tapped lightly with the wooden handle
of a small screw-driver, turning the needle in several different
positions while tapping.
Carburetor Fouled with Dirt or
Foreign Matter
No amount of dirt contained in the air supply can possibly interfere
with the action of the Stewart carburetor. As in any other type
of carburetor, however, if dirt, scale, or other foreign matter
works through the strainer, it may cause trouble.
To correct this, the instrument can be easily disassembled by
any competent mechanic and thoroughly cleaned. To accomplish
this, the carburetor should first be removed from the engine
and the outside thoroughly cleaned with gasoline or kerosene,
so that the dirt will not work into the inside when the instrument
is disassembled.
Next remove the float chamber cover and float; unscrew the strainer
plug at the bottom of the float chamber; remove the throttle
body or upper part, by means of two cap screws which attach it
to the main carburetor body, and also remove the gear housing
assembly (that is, the lowest part of the carburetor) by means
of the four screws which attach it to the main body. This will
expose the principal working parts of the carburetor.
If desired, the metering valve (M N L) can be disassembled by
catching the head (M) in a vise or holding same with a wrench
and turning the piston (L) to the left by means of a special
dowel wrench, which fits into two holes drilled in the lower
face of the piston. The head is attached to the stem by means
of a right-hand thread.
The carburetor body and disassembled parts should next he thoroughly
washed with gasoline and blown out with compressed air, if this
is available.
The metering pin, also component parts of the metering valve,
are very accurately machined and, when cleaning, no abrasives,
such as files, emery cloth or sandpaper, should be used. It is
only necessary to clean these parts to have them function properly.
In reassembling, take particular pains to note that the metering
valve is entirely free to slide up and down in the body of the
carburetor in any position to which it may be rotated.
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