Between the float chamber C and the engine connection of the carburetor is an enclosed space called the mixing chamber O. This compartment is provided with a valve for the ingress of free air.
Extending into the mixing chamber from a point below the surface of the gasoline in the float chamber is a passage, L for gasoline, ending with a nozzle, so constructed that gasoline drawn through it will come forth in a very fine spray. This is called the aspirating tube, atomizer, or more commonly, the spray nozzle.
The air inlet AA to the mixing chamber on the carburetor used on the Dodge is in the shape of a large tube extending from the carburetor to a box on the exhaust manifold. Air supplied from this source is heated in order that vaporization of gasoline may be more readily accomplished.
A cold air regulator is interposed between this tube and the carburetor proper so that in hot weather cool air may be admitted. This should always be closed when the temperature of the atmosphere is below 60 F.
The action of the carburetor is as follows: The suction created by the downward stroke of the pistons draws air into the mixing chamber through the air ducts (drilled holes HH). The same suction draws a fine spray of gasoline through the aspirating tube L (spray nozzle) into the same compartment, and the air, becoming impregnated with the gasoline vapor thus produced, becomes a highly explosive gas. In order that the proportion of air and gasoline vapor may be correct for all motor speeds, provision is made by means of a valve A for the automatic admission of larger quantities of both at high motor speeds. The ducts are open at all times, but the valve is held to its seat by its weight until the suction, increasing as the motor speed increases, is sufficient to lift it and admit a greater volume of air. The valve A is joined to the tube L, hence the latter is raised when the valve is lifted and the ingress of proportionately larger quantities of gasoline is made possible. This is accomplished by means of a metering pin P normally stationary, projecting upward into the tube L. The higher the tube rises the smaller is the section of the metering pin even with its opening, and hence the greater is the quantity of gasoline which may be taken into the tube. The carburetor thus automatically produces the correct mixture and quantity for all motor speeds.
The metering pin is subject to control from the dash, as will be explained later, by means of a rack N, and pinion M. To change the fixed running position of the pin, turn the stop screw to the right or left. Turning this screw to the right lowers the position of the metering pin and turning it to the left raises it. As the pin is lowered more gasoline is admitted to the aspirating tube at a given motor speed, thus enriching the mixture.
A wider range of adjustment of the position of the metering pin may be had by releasing the clamp of the pinion shaft lever and changing its position with relation to the shaft. This should never be attempted by any save experts in this class of work.
The carburetor used on the Dodge Brothers car is so nearly automatic in its action that it is not effected by climatic conditions, or changes in altitude or temperature. It automatically adjusts itself to all variations of atmosphere. It is, therefore, wise to see if the causes of any troubles which may develop are not due to derangements elsewhere than at the carburetor before attempting any changes of its adjustment.
Make all adjustments with dash adjustment all the way in.
The metering pin should not be tampered with unless absolutely necessary.