CARBURETORS: MARVEL
As soon as engine has fired, release choker. Run for a moment
until engine has warmed up, remembering to never use choker
more than necessary, as when not needed it has a tendency to
foul up engine and ruin the lubricating oil in the crank-case.
Next, set air screw for good idle by either turning in to the
right a little or backing out to the left as the needs of the engine
require, remembering that first of all, the needle must be set
as described.
With the needle so set and the engine warmed up, the adjustment
of the air screw for proper idling is easily accomplished by using
a little care.
If the air screw is turned in too tight, the engine will roll.
If the air screw is not tight enough, the engine will hesitate
and perhaps stop entirely.
To make a nice clean adjustment for idle, first having set needle
as described, turn air screw in quarter of a turn at a time until
engine does roll; then turn back to the left until engine hesitates,
indicating that mixture has too much air and is too lean; next
turn air screw in to the right threeor four notches at a time until
the engine runs smoothly.
This accomplished, the proper adjustment for the entire range of
the engine will have been attained, thus insuring the best economy
and power.
If the engine idles too fast with throttle closed, the latter may
be adjusted by means of the throttle lever adjusting screw.
Rich mixture: An over rich mixture will cause the engine speed
to "roll" or fluctuate through more or less regular periods
from high to low speeds.
Lean mixture: The best adjustment is obtained with the fuel and
air valve set as described. It must be remembered that too lean
a mixture as well as an over rich mixture causes overheating and
loss of power and is not as economical as an adjustment which provides
just the proper proportion of gasoline and air.
Float-level adjustment: Set so that distance from top of cork to
top of bowl is as follows: Model T, for Buick, i),"; Model
U, for Nash Advanced Six, Model UU, for Nash Special Six, ya";
Model N, used on Nash Special Six with seven bearing engine and
stamped brass fuel bowl, Al". To make adjustment, move float
lever which will raise or lower float.
MARVEL MODEL "UU" CARBURETOR USED ON NASH SPECIAL SIX
The principle of carburetion, heat control and adjustments explained
in the foregoing description of the Buick also applies to the Marvel
Models "U" and "UU" carburetors on the Nash
cars. The only difference lies in necessary construction changes
to adapt them to the Nash engines and in control levers and fuel
jet, etc. sizes.
Fig. 6. Two views of the Marvel model "UU" carburetor
as used on the Nash special six cars.
Names of parts are the same as on Figs. 1 and 2: (4) low-speed
nozzle; (5) gasoline adjustment needle; (6) high-speed nozzle;
(7) automatic air valve; (8) air screw; (11) fuel metering valve;
(12) throttle valve; (13) link connecting metering valve with throttle
lever; (14) choke butterfly valve; (N) inlet manifold connection;
(B) valve in heat outlet tube.
The model "U" as used on the Nash Advanced Six is practically
the same as the "T" (Buick)) on functioning of heat-control
system, except that levers are arranged slightly different.
MARVEL MODEL A-2S CARBURETOR USED ON OAKLAND SIX (1926) CARS
The Marvel model A2-S carburetor is of the automatic air valve,
two-jet type, with an economizer and accelerating device. It is
shown in illustrations, Figs. 7 to 11.
Adjustment of the air screw constitutes the only mixture adjustment
on the carburetor.
Economizer device: A further automatic control of the mixture is
provided by the "economizer" which is a metering pin
connected to the throttle lever which provides for a maximum power
fuel supply at wide-open throttle, and the very minimum fuel consumption
at all normal driving speeds at part open throttle.
The economizer remains in action on level roads up to approximately
50 m.p.h. and is entirely automatic and requires no adjustment.
Accelerating device: Also connected to the throttle and built in
with the economizer is the accelerating device. On quick opening
of the throttle a definite increased charge of fuel is forced from
the "high speed" jet to provide for quick "pick-up."
On top of the fuel bowl will be found a small lever pointing to "summer" or
to "winter." This provides for a maximum amount of accelerating
charge for cold weather when set on "winter" and a decreased
amount for warm weather when set on "summer," thus insuring
maximum "pick-up" under the two extremes of weather conditions.
This is not an adjustment, but a seasonal control only, and it
has nothing to do with the fuel supplied by the jets other than
the charge supplied on quick opening only of the throttle.
A choker button is provided for starting, located on the instrument
board. Pulling out this button closes a butterfly valve in the
air inlet of carburetor, restricting the air supply and increasing
the suction on jets, thus producing a rich mixture for starting.
Adjustment
First make sure that season heat control valve on intake and exhaust
manifolds is set correctly to provide the proper manifold heating
for winter or summer, providing on what the conditions are. Likewise,
look at the top of carburetor fuel bowl and see that the little
lever is properly set for "summer" or for "winter."
Engine must be run until thoroughly warmed up before proceeding
with final adjustment.
Set air adjusting screw so that same is flush with end of ratchet
spring bearing against it. Then obtain the proper idle setting
by turning air screw in a few notches until engine rolls through
richness, then turn out a few notches until engine falters through
leanness, and then midway between these two positions will be found
the proper setting.
Adjustment may be facilitated if made first at engine speed equivalent
to about 10 nt. p. h. on road, then checked after-wards at the
desired engine speed for idling for the final setting.
Caution: — Air cleaner must always be installed with "straightener
fin" in cleaner outlet vertical. Never attach cleaner with
this "fin" in any other position.
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