CARBURETORS : STROMBERG
went which gives the best feeling of power while the car is accelerating
through the 10 to 15 milesper-hour speed range.
After the low-speed wide open throttle power setting has been
determined, the mixture requirements for maximum speed at wide
open throttle should next be obtained by trial of different needle
settings.
If it is found that maximum speed and a quick pickup to maximum
speed can be obtained with a smaller high-speed needle opening
than was required on the hill, a smaller main discharge jet' or
a larger high-speed bleeder should be used for the "O" series
of carburetors and a large bleeder in the "M" series
of carburetors.
On the other hand, if a greater needle opening is required for
high speed, the main discharge jet of the "O" series
should be made larger or the high-speed bleeder made smaller, and
the air bleeder size of the "M" series decreased.
These changes should not affect greatly the setting required for
best hill performance, but to make certain the test mentioned in
the previous paragraph should be repeated until it is definitely
certain that the same high-speed needle setting will give the best
power without unnecessary fuel consumption at both low and high
speed.
Care should be taken in this test that the vacuum tank is high
enough above the carburetor to supply it adequately at full speed.
The next step is to find the level road normal speed-driving adjustment.
In making this adjustment, care should be taken that the idling
adjustment is not unduly rich.
Setting the hand throttle on the steering wheel to a position corresponding
to 20 to 25 miles an hour car speed in high gear on a level road,
try the high-speed needle adjustment to determine the point at
which the engine speed begins to fall away as the needle is closed
down.
The best adjustment for average service will usually be that giving
maximum engine speed for this throttle opening, but such that one
or two notches less needle opening will cause the engine to lose
speed.
If it is found that the adjustment previously determined for the
hill and high-speed performance is slightly too lean according
to these requirements, a smaller economizer reducer' (see Fig.
28B) should be used. If the best full throttle mixture adjustment
is richer than necessary for this part throttle operation, a larger
economizer reducer should be triek, until the needle adjustment
previously found rightfor hill and speed is also just right for
level road driving.
It should be remembered that no change of the economizer reducer
will affect the high-speed mixture so long as the economizer reducer
opening size is greater than the high-speed bleeder.
The final step is to adjust the idle. The low idle is the most
unstable part of the operating range of an engine and it is usually
essential that all valves be seating properly, that the spark plug
gaps be set to about .031", and that the intake manifold just
above the carburetor be at least warns to the touch, before the
engine can be made to idle steadily at a low speed.
In checking the range just off of idle, the points mentioned on
page where Fig. 26 is shown should be taken into consideration.
Accelerating Well Setting
The method of obtaining this setting for the Model "0" carburetors
is indicated on pages 1244-1249, and for the Models "OC" and "OS" carburetors
on pages 1250-1252.
It will generally be found that the standard carburetor settings
are satisfactory on the Model "0" carburetors: the amount
of accelerating discharge can, however, be cut down by using a
large accelerating well bleeder.
On the Models "OC" and "OS" carburetors the
accelerating well action can be cut down by the use of a smaller
well bleeder, but rather than reduce the size of this bleeder below
No. 6S or No. 70 drill, it is better to enlarge the holes in the
side of the well, or use a well of larger body so that there is
less space around it.
The accelerating well action usually determines the action of the
engine during the ten or twelve explosions first following quick
opening of the throttle. If the engine hits a tendency to stop
when the throttle is opened from low speeds, this tendency being
also shown when the engine is cold, the accelerating well action
is insufficient and should be in-creased.
If the engine, when warm, shows a tendency to stumble when the
throttle is opened just slightly from the idling position and this
tendency is not shown when the engine is cold, this is an indication
that the accelerating fuel capacity is too great.
Low-grade gasoline, a cold engine, intake manifold either cold
or of long and irregular shape, all require considerable accelerating
well action: while light gasoline, intake manifolds heated by the
exhaust, or short and small in diameter so as to give a high air
velocity, require much less well action.
HOW TO LOCATE ENGINE TROUBLES
The action of the carburetor is so intimately connected with other
elements of engine operation that engine troubles are often difficult
to diagnose, and the carburetor is often blamed for faults for
which it is not responsible.
When the engine misfires or refuses to start, after previous good
performance, the difficulty can always be located more quickly
by an orderly investigation of the different elements which are
essential to engine operation, as indicated in the following:
In particular, carburetor adjustment should not be changed until
following points have been investigated.
' See pages 1246—1248 for discussion of jet sizes.Make sure
that gasoline is reaching cylinders—see if gasoline (and
not water or other substance) is in carburetor float chamber—if
necessary inject gasoline through priming cock or spark plug hole.
3. Make sure a spark occurs—detach a wire from spark plug
and support it about %" away from some metal part of the engine,
and watch for a spark as engine is cranked. Make sure all other
wire terminals are attached.
4. Try the compression of each cylinder—turn off switch,
open throttle wide, and crank engine with hand crank.
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