The gasoline for low speed is taken in above the throttle through a jet at “K” and is regulated by dilution with air as controlled by the low speed adjusting screw “B.” Screwing “B” in clockwise gives more gasoline; outward, less. The best adjustment is usually 1⁄2 to 3 turns outward from a seating position. Note that this is only an idling adjustment and does not effect the mixture above 8 miles per hour. When motor is idling properly there should be a steady hiss in the carburetor; if there is a weak cylinder or manifold leak, or if the idle adjustment is very much too rich, the hiss will be unsteady.
The economizer device operates to lean out the mixture by lowering the high speed needle “E” and nut “A” a slight but definitely regulated amount at throttle positions corresponding to speeds from 5 to 40 miles per hour. The amount of drop and consequent leaning is regulated by the pointer “L.”
After making the high speed adjustment for best power, with pointer “L” in 0 notch, as above described, place throttle lever on steering wheel to a position giving about 20 miles per hour road speed. Then move pointer “L” clockwise (away from float chamber), one notch at a time, till motor begins to slow down. Then come back one notch.
The amount of economizer action needed depends upon the grade of gasoline and upon the temperature.
In the mid-west the best economizer adjustment will usually be the third or fourth notch. With Pennsylvania gasoline and in the South, the 2nd notch; while on the Pacific coast no economizer is necessary unless distillate (which should not be below 59 degrees Baume) is used. Also fewer notches economizer action will be necessary in summer than in winter.
CHAPTER V
“NITRO”-SUNDERMAN CARBURETOR
Fig. 34. Sunderman Carburetor
[Fig. 34] shows a through section of the new “Nitro”-Sunderman carburetor. This is practically a new model presented to the automobile industry for 1919 and 1920. It is claimed that it is an exact fulfillment of the long sought method of accurate compensation. It is of the single plain tube design with a single gasoline nozzle in the shape of a mushroom placed in the center of the air passage. Around this nozzle, however, rests the floating venturi which is a large end and small center floating air tube seen in [Fig. 35] which hurries the air at low speeds and checks the rush at high velocities. [Fig. 35] shows the commencement of action at idling speeds, and as the gasoline for idling comes from the same nozzle which furnishes the maximum power, an air by-pass is provided to reduce the suction on the nozzle at low speeds. The one single adjustment on this type of carburetor is shown at (X) in [Fig. 36], and is used only to control the passage of air through the by-pass at idling or low speeds. In [Fig. 34] the engine’s demand has increased to a point where the suction is greater than the weight of the venturi, which causes it to rise on the air stream, and open up the air passage around the head of the nozzle. This allows the compensation for the correct ratios of the air and gasoline mixtures.
