AS USED ON
SERIES 691 NASH SIXES
BOOKLET
S
MARVEL CARBURETER CO.
FLINT, MICHIGAN
U.S.A.
The carbureter measures the fuel charges for the engine andautomatically mixes them with the proper amount of air to form a highlycombustible gas. The Marvel Model "S" Carbureter is of the automatic airvalve, heat controlled type. Its outstanding advantages are:
1. Simplicity of construction and operation.
2. Quick starting in any weather.
3. Automatically controlled heat application to ensure completevaporization of fuels.
4. Economy in fuel consumption.
5. Ease of adjustment to meet varied driving and climatic conditions.
The construction embodies a main body or mixing chamber and aconventional float chamber bowl with fuel strainer attached at point ofentrance of fuel to bowl. Within the mixing chamber are two nozzleswhich proportion the amount of gasoline used in the mixture. One ofthese nozzles, called the "low speed," is regulated by the gasolineadjustment screw at bottom of carbureter and the other, called the "highspeed," is controlled by the automatic air valve. An air screw isprovided which regulates the pressure of the air valve spring enclosedtherein. Within this screw is also enclosed a plunger connected by alink to the air valve. The function of this plunger is to provide aresistance in addition to that of the air valve spring to assist inacceleration. This arrangement of plunger and air valve screw is termedthe dash pot.
A further control of the high speed jet is provided by the fuel meteringvalve operated by the carbureter throttle. This valve provides themaximum fuel feed to the "high speed" nozzle when the throttle is fullyopened for high speeds and for quick "pick up." During the ordinarydriving ranges this valve controls the amount of fuel being used, thusproviding all the economy possible. This valve is entirely automatic andrequires no adjustment.
The passage-way from the mixing chamber to the intake manifold iscontrolled by a butterfly valve which is called the throttle-valve andis connected to the throttle-lever on the steering wheel as well as tothe foot accelerator, its position determining the amount of gas and airor mixture being fed the engine.
A choke button is provided on the instrument board to assist instarting. Pulling out this button closes a butterfly choker valve (seecut) in the air intake passage of carbureter which restricts the airopening of the carbureter, and consequently produces a richer mixture.
To start engine, pull out choke button all the way. Advance spark leverabout half way and throttle lever about one-quarter way and depressstarter pedal.
As soon as motor fires when starting, this control should be releasedpart way, otherwise too much fuel will be drawn from carbureter, causingflooding of the motor and failure of the latter to continue to promptlyfire. After starting, motor should be allowed to run "part choke" asstated for a few minutes while warming up, then the choker controlshould be fully released, or pushed in completely on the instrumentboard, and engine allowed to run normally for sometime until water incylinder jackets is thoroughly warmed up before starting to make finalcarbureter adjustments.
In the colder seasons warm air is fed to air intake of carbureterthrough the warm air elbow "F" (see cut). This elbow connects thecarbureter with the warm air stove, which is