The Stromberg carburetor (Fig. 4C) is a double jet type, featuring an eccentric float chamber with a glass wall, a feature which is typical of all Stromberg models. The flow of gases is controlled by a butterfly valve placed over the mixing chamber and immediately over the ventnri, in which the main jet (I is located. The second jet, J, cornea into operation as the speed of the motor increases enough to permit the auxiliary air valve to open. The main air passage can be entirely or partially closed for starting purposes, and this operation also prevents the auxiliary air valve from opening, the latter being of the mushroom type, provided with two adjustments. The valve has two spindles. one above and one below the seat, each spindle having a spring encircling it. finer adjustment being claimed for this construction. The body of the carburetor is not water jacketed, heat being supplied through the open air pipe from a drum surrounding the exhaust manifold.
The features of the Carter carburetor, illustrated in Fig. 47, are eccentric float, shock-absorbing needle valve control and vertical multiple jet fuel tube. Gasoline enters the float chamber in the usual way. However, the needle valve is provided with a small shock-absorber, as no permanent connection is made between the float and the lever controlling this valve.
The tube, located in the funnel, has a multiplicity of small holes arranged spirally around the tube, and, as a vacuum is created in the carburetor by the suction of the motor, the fuel rises and falls instantaneously in the tube, according to the speed of the motor. As the fuel rises in the tube, it is sprayed out of the jets, and, owing to the minuteness of the jets and the force with which the fuel emerges, the gasoline is broken up into very small particles and converted into a mist. The spiral arrangement of the jets insures each one a separate supply of air. This fuel tube is adjustable for low speeds, while the intermediate adjustment is obtained through the auxiliary air valve. The high speed adjustment is an air control in the funnel carrying the fuel tube. A strangling tube connected with the float chamber is also provided for easy starting.
Many of the so-called carburetor troubles are not really the fault of the carburetor at all. Air leaks along the path of the gas in the cylinder will upset the action of the best carburetors made. The air leaks may be caused by defective gaskets between the manifold and the cylinder, or manifold and carburetor, or by loose studs, nuts or cap screws in these connections. These air leaks destroy the quality of the mixture, and also reduce the vacuum created by the motor, so that a much smaller charge enters the cylinders. Mixture proportion may also change, due to some disarrangement of the auxiliary air valve, as by the slackening of the nuts controlling the spring. On the present day models this difficulty is overcome by locking these nuts with split pins. Another source of trouble is the stoppage of the feed line from the tank to the carburetor, due to foreign matter in the gasoline. There is a noticeable tendency this year towards the use of strainers to remove these impurities.
The general concensus of opinion among the makers of carburetors is that, for commercial car motors, the mixture should be heated by some means before entering the cylinders. There are numerous ways of accomplishing this, by water jacketing the carburetor or intake manifold, and by supplying heat from the exhaust manifold, either directly to the mixture, or by a heat jacket around the mixing chamber of the carburetor.
Carburetors are made with or without water jackets, while the hot-water supply is generally taken from the pump through a small pipe and returned to the cylinders. The flow is controlled by shut-off cocks, so that it may be shut off during the summer months, when better results are obtained without the aid of heat. Hot air from the exhaust manifold may be circulated and controlled in a like manner.
In some motors, part of the intake manifold passes through the water jacket of the cylinders, so that heat is supplied to the charge. The direct method is by connecting the main air pipe of the carburetor with a drum, placed around the exhaust manifold, so that the air is always preheated.
It is quite difficult to state which of the above methods are the best, as this is to some extent dependent upon the design of the carburetor. One method might work well on a certain carburetor and absolutely fail on another make.
Carburetors are generally bolted to flanges of the intake manifold; however, the heavy vibrations existing in commercial car operation have led some makers to provide separate brackets on the crank case of the engine to take the weight of the carburetor and to prevent the adjustments from becoming disarranged due to the vibration.
Fig. 46. Sectional View of Stromberg Carburetor.
Fig. 47. Carter carburetor in Section.