Carburetter

Returning to our subject, the illustration herewith depicts a section of a new automatic carburetter designed by Mr. E W. Lewis, and called the “Rover,” from its being manufactured by the Rover Cycle Co., of Coventry. The principle to a certain extent is novel, in that not only is the additional air admission regulated, but that passing the jet is also regulated in volume and velocity. Referring to the drawing, A is the float chamber, which is of the usual construction. B is the body of the carburetter containing the mechanism for the automatic action. This is constructed so that there is a partition between the jet chamber and the mixing chamber above. The body B contains a brass liner, which is accurately bored to receive the plug C, and its upper portion is litted to the piston E, having a single ring packing at its lower edge. E is free to move vertically in the liner, and is screwed to the plug C, the two being attached to the rod I by a pin transverse to the plug, and passing through the boss in the carburetter cover. The piston E has triangular air ports H cut in it, which are proportioned very accurately lor their purpose.

The plug C is made heavy, and gravity is substituted for a spring in order to return the plug and piston to their normal position in which they are shown. Through the plug C are drilled the oblique radial holes, there being six rows of these, each row containing more holes than the one above it. It will be noticed that the two upper rows are above the level of the jet D, and open into the mixing chamber between the piston E and the base of the liner. When the engine is running, the reduction of pressure, or rather partial vacuum, in the mixing chamber raises the piston E and its attached plug C, thus increasing three proportionate dimensions of the carburetter, viz., the number of holes, or, if the difference is small, merely the area of the holes immediately beneath the liner through which air is drawn past the jet; the cross-sectional area of the orifice between the jet an the walls of the plug through which the initial air has to pass: and, lastly, the area of the additional openings at H, and, therefore, the quantity of mixture which is sucked through the four triangular openings which increase the area of the outlet to the engine in proportion to its speed. Thus a difference in pressure immediately distributes itself into a vacuum balance affecting directly the volume of the air admitted to the carburetter, and, beyond this, equally important, the velocity at which such air is admitted.