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narrower than the total angular travel of the mixture
metering valve.
To obta:in the full benefit of the
idle shut-off feature, with the engine idling, push the
mixture control lever to the full lean position and
allow the engine to stop from lack of fuel before
shutting off ignition, thus assuring that the cylinders
are dry of fuel.
(7) Use of Mixture Control.
When adjusting mixture control, move control in and out
slowly with the throttle at Cruising or Full Open Position
until the highest R.P. M. is attained. The carburetor
mixture will then be correctly adjusted for all throttle
positions and loads at that particular altitude.
Always have mixture control in the full rich
pOSition when coming in for a landing, so that
if
full power is required in an emergency near
the ground the engine will operate satisfac-
torily and will not over-heat because of too
lean a mixture.
(8) Adjustment of Carburetor.
H,
after checking all other points on engine, it is
found necessary to readjust the carburetor, proceed
as follows:
With engine thoroughly warmed up, set Throttle
Stop Screw so that engine idles at approximately
550 R.P.M. Turn Idle Adjusting Needle out slowly
until engine "rolls" from richness, then turn needle
in slowly until engine -"lags," or runs "irregularly"
from leanness.
This step will give an idea of the
adjustment range and of how the engine operates un-
der these extreme idle mixtures.
From the lean
setting, turn needle out slowly to the richest mixture
that will not cause the engine to "roll" or run un-
evenly. This adjustment will in most cases give a
slower idle speed than a slightly leaner adjustment,
with the same Throttle Stop Screw setting, but will
give smoothest idle operation.
A change in idle
mixture will change the idle speed and it may be
necessary to readjust the idle speed with Throttle
Stop Screw to the desired point. ';I'he Idle Adjusting
Needle should be from 3/4 to 1 turn from its seal to
give a satisfactory idle mixture.
48
Care should be taken not to damage the idle
needle seat by turning the idle adjusting
needle too tightly against seat, as damage to
this seat will make a satisfactory idle ad-
justment very difficult.
(9) Float Height (3, Fig. 32.)
The float height is set at the factory, and can be
checked by removing the throttle body and bowl cover
and float assembly and turning upside down. Proper
setting of the two floats should measure 7/32" from
bowl cover gasket to closest surface of each float.
Be sure to check both floats to proper dimenSions,
making sure that the floats are parallel to the bowl
cover gasket.
(10) Starting - Cold Engine.
With mixture control in full rich pOSition prime
the engine as directed by the engine manufacturers
instructions and set the throttle approximately 3/32"
from the throttle stop screw. With the throttle in this
position, turn the engine over two or three times be-
fore ignition is turned on. This will draw a finely
emulsified mixture of air and fuel through the mani-
fold into the combustion chamber, then if the ignition
is turned on, the engine should start on the next turn
over and with the throttle stop 3/32" from the
throttle stop screw there should be sufficient throttle
opening to keep the engine running. The carburetor
is calibrated to give the richest mixture at this
throttle opening, and therefore,
a cold engine will
run the smoothest with the throttle in this position.
For this reason the engine should be allowed to
warm up for several minutes before opening the
throttle further.
(11) Starting - Hot Engine.
To start a warm or hot engine, put mixture con-
trol in fuil rich pOSition and pull the throttle stop
back against the throttle stop screw.
H
the ignition
has just been shut off, turn on the ignition and the
engine should start on the first turn, but if the engine
has been shut off for several minutes,
it
may be
necessary to turn the engine over once or twice be-
fore turning on the ignition. A warm or hot engine
should start and continue with the throttle in the
idling position.
Do not open and close throttle in starting as
this is likely to deposit raw gasoline in the
carburetor air box and constitute a definite
fire hazard. Do. not prime a hot engine.
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