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small,
round
brass
disc
riveted
,to the car!Juretor.
The
Zenith
carburetor
supplied
on the
l.Iodel 250,
155 II. P. Knight
may require
adjustment
of
the
throttle
plate
stop scre'w
"An at
the
full throttle
position
(See
Fig. 69.) This carburetor is some-
'7hat
sensit ive
to
the
thrott Ie
plate
positioning
in that
if
it
goes
slightly
past
the
vertical
POSition,
it will
upset fuel dis-
tribution in the
~anifold
and cause
~~
l!Iar!ced
decrease in
engine p017er
and speed
at
full
throttle.
The
carburetor is
correctly set on en-
gines
tested at
the factory,
but
replacement
carburetors '"/ill
have
to be adjusted in the field.
l7ith
the
carburetor
attached and
the engine
ready
to run,
loosen
the stop
screw "A"
until it
does
not contact
the stop pin f'B"
with
the throttle lever
"c"
at the full
throttle position' as
sho~m
in Fig.
69.
In this position
the cast lug
on the throttle
lever should touch
the stop pin.
Now with the
engine
running at
full
throttle,
close
the throttle very slowly
and care-
Fig.68
Carburetor - Adjustoents
-53-
fully observe
the reaction
of the
tachometer. If the tachometer shows
a steady
decrease as the
throttle
is retarded,
the stop screw is not
needed in adjusting the carburetor.
Ho~ever,
if the
tachometer
first
increases
to a
maximum
and
then
falls
off as the
throttle is
re-
tarded, the stop screw must be used
to correctly position the throttle
plate as follo'rls: Find the thrott Ie
position that will give maximum en-
gine RP:U and stop the engine without
disturbing
the
throttle
setting.
Screw
the stop
screw in
until it
just touches the stop pin.
Restart
the
engine and
check to
see that
it uill
still attain its
peak RPU
as noted before the adjustment.
It
would be preferable if the
adjust-
ment or setting
of the
stop screw
't7as made
with the
engine running,
but this is
not possible or advis-
able in many installations.
Always take every precaution against
fire
hazards
when working
around
your fuel system.
Be sure
to dis-
connect batteries;
do not
turn on
flashlights,
operate
electric
switches
or turn
over the starter
or generator.
THROTTlE LEVER "C" IN
FULL THROTTLE POSITION
~_J
Fig.69
Carburetor - Adjustments
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