Putnam's Automobile Handbook: The Care and Management of the Modern Motor-Car

by H. Clifford Brokaw; Charles A. Starr

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 operation 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. One little, good-for-nothing, insignificant speck of dirt, so small as to be almost invisible, will put the best carburetor literally out of business, and the only thing to do is to remove the speck.

There are several good makes of gasoline strainers which reduce this trouble to a minimum, provided one will drain off the strainer occasionally to let the dirt run off. Straining the gasoline supply through wire gauze or chamois does not obviate the difficulty, for gasoline tanks are prone to acquire a slight sediment.

A few drops of water in the gasoline which reaches the carburetor will make trouble likewise, for it will not vaporize, and, what is more, it will not let anything else vaporize. Probably no one is trying to dilute the gasoline with water and sell you such a mixture, but there are some mighty careless men in the gasoline trade. It reminds one of the farmer caught selling watered milk, who pleaded that there was a pump in the milking yard and some of his men must be careless in passing by it. The chamois skin will remove this impediment, for water will not pass through it.

Another trouble which afflicts motor-boat engines more than the automobile motor has to do with the weather. The motor-boat carburetor requires frequent adjustment, due to changes of the weather. On a dry, warm day the gasoline vaporizes easily and the maximum charge is readily exploded in the cylinder, giving a maximum of power. On a wet, cold, heavy day, one must slightly decrease the supply, or the cylinders will clog, the engine will knock, and one will think harsh things if they are not audibly expressed. The automobile engine, not being so constantly over the water, will not have this trouble so much, but it is probable that most drivers fail to take this into consideration and perhaps do not know that it is a cause of trouble.

A very slight leak in the intake manifold gaskets likewise makes all sorts of trouble, since the supply of mixture to the cylinders will vary according as the vibration opens up the gasket and stops the suction by which the cylinders are supplied. A leaky piston ring will do this for one of the cylinders. If worn, or frozen fast by carbon, it will fail to keep the piston tight, the mixture passes by the leak, if sucked in, and there is no compression and no explosion or irregular firing. This will make one think sometimes that the carburetor is at fault, whereas the engine really needs an overhauling.

In fact, if one is having engine trouble which is hard to diagnose, one should try out the piston rings to see if they are doing their duty. This is very simple, for all practical-test needs. Crank the cylinder up to high pressure and let it stand a couple of minutes. Then open pet or priming cock and see if there is any pressure left. On the two-cycle engine this is a good test, and by trying the cylinders in turn piston ring trouble may be located.

On the four-cycle engine the valves must be considered also, for they may leak and the pistons be perfectly tight, but in such an event it will be found almost impossible to get good pressure on the cylinder, since it leaks through the valves while the piston is making the compression stroke. Don’t condemn the carburetor until you have determined whether either of these things is occurring.

The carburetor should be drained occasionally to prevent the accumulation of sediment, which will later clog the needle valve, and at least once a season should be taken apart and cleaned. Time spent in this way well repays the owner.

In all that has been said thus far no account has been taken of poor gasoline. By this is not meant gasoline with water or dirt in it, but a poor quality. Nowadays there is such a demand for gasoline for automobiles and motor boats, that the producers have had to market much of a low grade, or, as is generally the case, have mixed the first quality with the cheaper grades, producing a medium quality.

The seeming necessity of utilizing these low grades of gasoline makes it necessary to change the carburetor forms, and one sees now a tendency to do away with the old, long intake, either by raising the carburetor to the cylinder level, with a horizontal intake only, or with an internal intake manifold, the carburetor being attached to the cylinder block. Several makes of carburetors using one of these methods are said to vaporize even the low grades of gasoline, while some later models are claimed to handle kerosene successfully.