Fig. 38. Schebler Model R Carburetor Assembled

Model R Adjustment.—To adjust this carburetor turn the air valve cap to the right until it stops, then to the left one complete turn, start the motor with the throttle 1⁄4 open; after it is warmed up turn the air valve cap to the left until the motor hits perfectly. Advance throttle 3⁄4 on quadrant. If the engine backfires turn screw (F) up, increasing the tension on the air spring until acceleration is satisfactory.

CHAPTER VI
THE STEWART CARBURETOR

[Fig. 39] shows the Stewart carburetor used on Dodge Brothers cars, which is of the float feed type in which a fine spray of gasoline is drawn from an aspirating tube by a current of air induced by the engine pistons. The supply of gasoline being regulated by a float which actuates a needle valve controlling the outlet of the feed pipe. This tube is also called the spray nozzle. This type of carburetor is commonly used on automobile engines.

It consists of a float chamber containing a float, functions of which are described below, a mixing chamber in which the gasoline spray is reduced to vapor and mixed with air (i. e., “carbureted” in proper proportion).

The float and valve maintain a constant or even supply of gasoline for the carburetor.

The gasoline flows from the filter Z into the float chamber C through the inlet valve G, which is directly actuated by the float F, so that it closes or opens as the float rises or falls. As the float rises the valve is closed until the float reaches a certain predetermined level, at which the valve is entirely closed. If the float falls below this level because of a diminishing supply of gasoline in the float chamber, the valve is automatically opened and sufficient fresh gasoline is admitted to bring the level up to the proper point. From the foregoing it will be seen that the float chamber in reality serves as a reservoir of constant supply, in which any pressure to which the gasoline has been subjected in order to force it from the tank is eliminated. When the engine is running gasoline is, of course, being constantly drawn off from the float chamber through the aspirating tube L, as will be described later, to meet the requirements of the motor, but in practice the resulting movement of the inlet valve is very slight and hence the flow of gasoline into the float chamber is nearly constant.

The gasoline inlet valve is also called the “needle valve.”

Fig. 39. Stewart Carburetor