CHAPTER IX

THE CARBURETOR AND ITS FAILINGS

One of the frequent and most annoying troubles to which automobile engines are subject has to do with the carburetor. With one of the standard carburetors or vaporizers which is properly adjusted there should be, and usually is, no serious difficulty in ordinary conditions, but if there is one part of the engine which seems possessed to kick up its heels it is the carburetor. Particularly is this so in the frosty months, when the gasoline and air do not mix properly and do not vaporize when they do mix. This is of easy solution, however. Simply warm the intake a few minutes and it will take care of itself thereafter.

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.

For the motor boat there are several makes of vaporizers which will handle either gasoline or kerosene, and all intermediate grades, by slight adjustment. It is possible that some ingenious builder will devise a similar vaporizer for the automobile engine, if gasoline continues to decline in quality, and to be short in supply as well.

An easy test to see whether the carburetor is working right is to run several blocks with the throttle practically closed, then, when the road is clear, press sharply upon the accelerator pedal, which opens the throttle wide and should make the engine speed up and the car jump forward. If it is sluggish it will denote a too rich mixture, and if it sputters and perhaps backfires, it is too lean. But if, with smooth yet rapid action, it makes the car speed up, that is “pep.” The amount of pep which a car is said to possess is gauged by the quickness with which it responds to the acceleration, either by the pedal or by throttle lever, changing the car from slow or moderate speed to full speed. That, too, without jerky action or tearing the motor apart.

While this test, showing the presence of pep, will denote that the mixture passing through the carburetor is correct, absence of pep does not always mean that it is wrong. Therefore it is not wise to jump to the conclusion that the adjustment is wrong. In fact the adjustment should not be changed unless it is fully certain that it is wrong. If the car has been running with the carburetor working properly and no one has changed the adjustment, it may safely be assumed that the carburetor adjustment is correct. Adjustments are not changed except by someone’s fingers.

Do not be like the new chauffeur who, having trouble, at once descended upon the carburetor. Another chauffeur whose car was standing near advised:

“I wouldn’t touch that, boss.”

“Well, there’s something the matter and I guess it’s here,” said the troubled one.

“I wouldn’t touch it, boss; try somewhere else.”

“Oh; let’s see what’s on the inside of it,” impatiently exclaimed the new chauffeur, and he proceeded to unscrew and unbolt the parts.

Of course, he had to send to the garage for a repair man and finally was towed in for complete reassembly and readjustment of the part.

The lesson in all this for the owner is that he should learn the make-up and peculiarities of his carburetor, understand its common and uncommon ills and thus be able to remedy a trouble which would mar a trip or the general serviceability of the car. 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.