Carburetor

“ A carburetor must thus have an additional device that will keep the mixture correct, regardless of the speed at which the engine runs. This is sometimes done by changing the size of the spray nozzle so that a greater or less quantity of fuel flows out, but more usually by permitting an extra quantity of air to enter the carburetor as the engine speeds up. ”

“ The design of a carburetor is a complicated matter, because the [Pg 66] production of mixture is due to the flow of air, which is a very changeable thing. On a cold, damp day, the air will be heavier and denser than on a day that is hot and dry, and different quantities of fuel will be necessary for the formation of the mixture. The carburetor manufacturer cannot make a commercial carburetor that will take care of such a difference as this; he strikes an average that gives good general results, and expects the user to change the adjustments when weather and temperature make it necessary. ”

“ Fig. 26 shows a longitudinal section of a type M plain tube carburetor, and shows the location of the gasoline when the motor is at rest. The various parts are indicated by names and arrows. An elementary requirement of a carburetor is that as a metering device it shall properly proportion the gasoline and air throughout the entire operating range.
Fig. 27. Stromberg Carburetor Model M—Air Bleeder Action
In the carburetor under discussion this mixture proportioning is properly maintained by the use of what is termed the air bleed jet. ”

“ The modern carburetor is sufficiently automatic in its action to provide the proper mixture within wide ranges of speed change of the motor, but even nowadays it is often found necessary to increase the gasoline supply or to reduce the amount of air admitted to the intake pipe whenever it is desired to throttle the motor down to a very low number of revolutions per minute. ”

“ One that carburets; specif., an apparatus in which air or gas is carbureted, as by passing it through a light petroleum oil. The carburetor for a gasoline engine is usually either a surface carburetor, or a float, float- feed, or spray, carburetor. In the former air is charged by being passed over the surface of gasoline. In the latter a fine spray of gasoline is drawn from an atomizing nozzle by a current of air induced by the suction of the engine piston, the supply of gasoline being regulated by a float which actuates a needle valve controlling the outlet of the feed pipe. ”

“ Carburetor is of the side‐outlet, plain‐tube type with a fixed venturi. Fuel feed is by gravity from tank above. Carburetor has two manual controls: the throttle, which is operated by the right handle bar grip, and the choke, which is operated by a lever on the carburetor itself. The high speed fuel supply is governed by a fixed (non‐adjustable) jet. The idling to medium speed (30 mph) fuel supply is governed by an adjustable (low speed) needle valve located on rear side of carburetor body. ”

“ Carburetors are built so that the float valve and spray nozzle may be easily cleaned, for by withdrawing plugs fine wire may be run through them. When a carburetor is taken apart for more thorough cleaning, the position of the gasoline and air adjustments should be remembered, in order that they may be replaced in approximately the correct positions, thus saving time in making the adjustments that will be necessary. ”

“ In the simple carburetor described, the speeding-up of the engine will result in a greater rush of air through the intake pipe, which in turn [Pg 63] will suck out a much greater quantity of fuel. If the carburetor is adjusted to give the proper quantity of fuel for the air that passes at low speed, at high speed it will give far more fuel than will be required by the quantity of air that then passes. Thus at high speed the mixture will be too rich. ”

“ Having determined the point where the motor runs at its maximum speed, the needle valve lock nut should be tightened to prevent the adjustment being disturbed. For average running a lean mixture will give better results than a rich one.
Q. Why does water clog the carburetor?
A. The presence of water in the carburetor or gasoline tank, even in small amounts, will prevent easy starting and the motor will misfire and stop. As water is heavier than gasoline it settles to the bottom of the tank and into the sediment bulb along with other foreign matters. ”

“ The purpose of repeating this caution as to mixture thinning is to make it plain that wherever there is a leak between the carburetor and the cylinder it lets in air and thins the mixture so that it is necessary to feed in more gasoline to get a mixture that will fire and that is wasteful, for a mixture made anywhere else than in the carburetor is less efficiently accomplished. ”

“ Have you tried the little valve forward of the carburetor?"
"Why, no," rejoined Merritt; "but I hardly think—"
"It wouldn't be the first time a carburetor had fouled, particularly after what we went through in that squall," remarked Tubby. "It's worth trying, anyhow." ”

“ The simple carburetor illustrated in Figure 21 can be adjusted to give a correct mixture for any particular speed, but will be out of adjustment for any other speed.
The speed of a 1-cylinder engine does not change very greatly; it is built to run at practically a constant speed, and a simple carburetor is satisfactory for it. The speed of engines with a greater number of cylinders may be greatly changed, and the carburetor must be so made that it will give the same proportions of vapor and air at low speed as at high. ”

“ Remove fuel strainer assembly from carburetor bowl nipple.
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71. CARBURETOR INSTALLATION. a. When installing carburetor be sure to fit the 1⁄2–inch thick steel spacer (if one was originally fitted) between carburetor and manifold flanges, with two gaskets on one side and one gasket on the other side. Later models have a longer manifold neck, extending carburetor farther to the left, away from cylinders, and do not need the spacer.
(1) Install fuel strainer assembly on bowl nipple. Leave coupling nut loose until after fuel pipe is connected. ”

“ Attached to the motor are the carburetor, in which air and gasoline are mixed properly for rapid combustion, wires to supply ignition to the mixture at the proper time, a device for giving lubrication, and exhaust pipes leading to the muffler, the latter designed to stifle the noise of rapid explosions, which otherwise would be deafening. ”

“ Besides the possibility of getting out of adjustment, the greatest trouble with a carburetor comes from the clogging of the passages and openings with dirt. When dirt enters, it clogs the gasoline inlet valve and prevents it from seating properly, the float chamber being flooded as a result. When the level in the float chamber is raised, more than the required amount of gasoline flows out of the spray nozzle, and the mixture that is produced is too rich. ”

“ Turning one disc by means of a small handle outside, so that the four outer holes cannot coincide with those in the other disc, decreases the flow of air and causes all air to rush through the center hole, where the tiny carburetor tube passes through. The present carburetor was transferred over from the first engine. When Frank later installed the engine on the carriage he noticed the close proximity of the intake pipe to the open end of the muffler. ”

“ It is unnecessary to go into the detail of any make of carburetor, because if the manufacturer’s instruction book does not contain full information and sketches of the make used, a special carburetor book may be obtained from the maker. But there is no excuse for failure to master the lungs of the engine and to learn how to keep them breathing properly. ”

“ If the carburetor flushes easily, it is evident that there is no serious stoppage in the pipe. If this easy flushing is followed by good running on the part of the motor, and if this, in turn, is succeeded by gradually-diminishing impulses indicating a weakening mixture, it is quite evident that the float is preventing the flow of the gasoline at the proper time. ”

“ In these days of indifferent gasoline automobile drivers are complaining constantly that the carburetors are giving unusual troubles. The carburetor is the lungs of the engine. Well, did you ever breathe in a crumb of cake and then for a while have all your faculties suspend operation52 while the lungs sought to expel the intruding substance? That is just what happens when you get a crumb of something in the needle valve, or in the intake valve of the vaporizer. ”

“ Before attempting to adjust carburetor to correct faulty engine performance, attention should be given other items which have a direct bearing on and can affect carburetor adjustment as well as engine performance. ”

“ Fig. 22 shows an actual sectional drawing of a carburetor used on a four-cylinder motor. In this particular carburetor, however, the float chamber and float surround the mixing chamber, and the float valve, instead of being directly under the float, is at the right hand side and is operated30 by means of a lever. The needle valve, which is the little round rod having a “T” handle, running up through the center of the mixing chamber, controls the amount of gasoline flowing from the gasoline chamber to the nozzle. The air comes up through the bottom and around the gasoline jet. ”

“ A bell crank rocker arm acts on the valve stems which in turn is actuated through a push rod that extends from the cam-shaft in the crank chamber. The cam-shaft, rocker arms, valves, and half time gears are clearly shown by Fig. 128. The housings of the inlet valves connect directly with the special kerosene carburetor made by the Rumely Company. The Higgins carburetor used on these engines is very simple and effective in vaporizing the heavier fuels and has no springs nor internal mechanism to get out of order. ”

“ An engine is always started on gasoline, for that will form a mixture when it is cold. Before switching to kerosene the engine must be hot, and this will take several minutes of running on gasoline.
With a double carburetor, which has a separate fuel bowl and spray nozzle for each fuel, nothing more is required than the switching of one or the other into action; when the two parts have once been adjusted, they require no further adjustment. ”

“ On a cold, damp day the fuel will not vaporize in the carburetor to any extent, and much of it will pass to the cylinder in drops that even there will not vaporize in time to form a mixture. In order to assure the vaporization of enough fuel to form a mixture under such conditions, the fuel and the air must be heated to a greater degree. ”

“ The flow of gasoline entering the carburetor through the feed pipe is automatically regulated by the float needle raising and lowering in its seat. Should any particle of dirt become lodged in the seat, which prevents the needle from closing, the gasoline will overflow in the bowl of the carburetor and leak out upon the ground. ”

“ If the engine misses fire, or runs irregularly, the loss of power will be due to faulty carburetion or ignition. The mixture may be too rich or too lean; in either case the trouble will be remedied by readjusting the carburetor. A mixture that is very much too lean will make itself known by backfiring; there will be little explosions at the carburetor. This should be remedied at once, for the danger of fire from it is very great. Black smoke at the exhaust is a sign of a mixture that is too rich. ”

“ The gasoline supply tank is seen on the left-hand side of the testing frame, as viewed in Plate 82, the carburetor being placed below it and the gas supply pipe from the carburetor passing through the gasoline tank. Instead of jacketing the carburetor, a grid formed of thin copper tubes is supported just above the multitude of small air pipes leading into the carburetor, and some of [p249] the hot water from the engine is by-passed through this grid and thus warms the air as it passes into the carburetor. ”

“ Very frequently they will allow the supply of gasoline in the carburetor to run nearly out before they replenish it, in which case the gas comes to the burners in a thinner quality, and in order to provide the same volume of heat, it is necessary to adjust the burner valves and throw a larger stream of gas into the burner. ”

“ If the engine has been running, it is practically certain that the carburetor has not gotten out of adjustment. Inspect the intake pipe, or manifold, to see if it has been loosened by vibration. If the engine still refuses to run, put about a tablespoonful of gasoline in each cylinder and crank over the engine. ”

“ Numerous cases are on record in which cylinder heads have been blown off or castings cracked by the force of some of the explosions when too much "dope" has found its way into the mixture.
Although the average motor gasoline obtainable nowadays is hardly all that could be desired as automobile fuel, a little care taken when filling the tank will eliminate many of the carburetor annoyances to which many cars seem to be subject. ”