The automobile owner's guide

by Frank B. Scholl

STROMBERG MODEL L CARBURETOR

There are three adjustments; the high speed, the extremely low speed or idle, and the “economizer.”

The high speed is controlled by the knurled nut “A” which locates the position of the needle “E” past whose point is taken all the gasoline at all speeds. Turning nut “A” to the right (clockwise) raises the needle “E” and gives more gasoline, to the left, or anticlockwise, less.

Fig. 33. Stromberg Model “L”—Adjustment Points

If an entirely new adjustment is necessary, use the following practice. Put economizer “L” in the 5th notch (or farthest from float chamber) as an indicator, turn nut “A” to the left, anticlockwise, until needle “E” reaches its seat, as shown by nut “A” not moving when throttle is opened and closed. When needle “E” is in its seat it can be felt to stick slightly when nut “A” is lifted with the fingers. Find adjustment of “A” where it just begins to move with the throttle opening, then give 24 notches to the right or clockwise (the notches can be felt). Then move the economizer pointer “L” back to the 0 notch (toward float chamber). This will give a rich adjustment. After starting and warming up the motor, thin out the mixture by turning “A” anticlockwise, and find the point where the motor responds best to quick opening of the throttle, and shows the best power.

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.

Fig. 35. Sunderman Carburetor

In [Fig. 37] the venturi closes the air by-pass and under full suction, gives the maximum area around the nozzle for leaner mixtures and full volumetric. The unrestricted air passage in the plain tube type of carburetor is here worked out to its fullest development.

Fig. 36. Sunderman Carburetor

The Venturi.—This is a stream line air passage tapered to a narrow throat near the center which increases the velocities without offering a restriction to the free air passage, and being of a very loose fit in the carburetor, is allowed to float up and down on the air stream around the nozzle over which it automatically centers at all times. The venturi goes into action slowly as it is retarded by the action of the air by-pass, but rises fast when the latter is cut off. It rides on the air stream at a perfect balance and offers no resistance to the air passage because of its stream line taper, and as the venturi float is sensitive to a fine degree, it is ready for any change in the motor suction and compensates accordingly. The jet tube running up into the mushroom head contains a jet which is drilled for the particular requirements of the motor on which the carburetor is installed. This jet feeds into the mushroom head which is drilled with four small holes which spread the gasoline by capillary action in a fine fan film to all sides of the under surfaces of the slot. Here the ascending air picks it off at right angles to its path in a very fine vapor. This vapor is carried up the stream line venturi without cross currents and is in a finely mixed state of flame-propagation. The heavier fuels are readily broken up with this nozzle and straight kerosene has been used with success. This carburetor does not require any other care than a thorough cleaning out once or twice in a season.

Fig. 37. Sunderman Carburetor