Carburetter Troubles.

Progress, Volume V, Issue 5, 1 March 1910, Page 159

Carburetter Troubles.

clogged petrol filter, poor petrol, leak in supply pipe or intake manifold, weak or rich mixture. Symptom : Engine difficult to start. Causes: Fuel tank empty, petrol supply cock shut off, rich mixture, weak mixture, dirt or water in carburetter, engine and carburetter cold, fuel supply pipe obstructed, air in petrol feed pipp, petrol level too low in float chamber. Although this is not a complete list of all the possible troubles which might occur, it covers practically all of those difficulties which may be traced to lack of care and improper adjustment. As to mixture, the quality of this is one of the chief causes of trouble and the right mixture for every car is a matter for observation and experience in each case, helped bv systematic experiments. Mixture may lie too rich (with too much petrol) or too poor (with too little). One advantage of a rich mixture is the better speed due to it. The disadvantages are quick fouling of cylinders, pistons, and valves with soot, overheating of cylinders. and sometimes waste of fuel. At lov/ and medium speeds rich mixtures are apt to choke and misfire, and they fail to respond to the throttle. Lean mixtures, on the other hand, fail for lack of power; thdv run smoothly and well enough at low speeds, but at high speeds they misfire and tend sometimes to slow down and stop. A lean mixture usually produces a loud popping noise When this occurs, increase the proportion of fuel.

Water in the Carburetter. "Water in the carburetter or in the petrol is often the cause of much annoyance, and its presence in even very 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, so when the motor has been standing for any length of time it is a good plan to drain the carburetter by opening the cock at the bottom of the float chamber. The careful driver will prefer to take a little extra trouble and filter the fuel while filling the tank. A piece of chamois skin inserted in the funnel will catch any water or other foreign substance that may be in the fuel, and so prevent future trouble, and is better than the finest gauze. Stale petrol or petrol of low grade possess greater density than a good or high grade spirit. Petrol becomes stale through evaporation, and, owing to the loss of the lighter parts of the fuel, stale petrol is not fo readily converted into vapour. Stale fuel will not usually seriously interfere with the operation of the motor, but it occasionally prevents an easy start. It is in part for this reason, that priming, filling the carburetter with fresh fuel, is often resorted to when starting a cold motor.

How to Adjust the Carburetter. Stillman Taylor is one of the best authorities on this subject. This is what he has written : — Carburetters are now made in a great variety of forms, and as a great many cars are provided with carburetting devices of individual and exclusive design, it would be impossible to even mention the different types in an article of this length. Practically all modern carburetters are constructed on the float-feed principle, in which the petrol level in the float chamber is controlled by the buoyancy of a light

metal or cork float. A few designs of carburetters are automatic in action, but the prevailing types are provided with an adjustable screw needle valve for regulating the petrol feed. Two air inlets are generally provided, one being a fixed air inlet or by-pass which is always open, and the other an auxiliary nir valve. The object of this auxiliary air inlet is to automatically supply, additional air as needed at high motor speeds. In many carburetters this function is automatically performed by moans of a mushroom valve balanced by a helical spring against the suction. The' tension of this spring may be regulated to suit varying conditions, and the valve is opened by the suction of the pistons in a manner similar to the automatic intake valve. That the petrol may be uniformly vapourised in cold weather, carburetters have some way of heating the fuel, either bv surrounding the mixing chamber with a jacket and circulating hot water or hot air through this space, or by means of a hot air box through which the air must pass before it enters the mixing chamber to be mixed with the gasoline. Different carburetters are adjusted in a different manner, and as almost all manufacturers issue an instruction book covering the adjustment and maintenance of their car, the reader should consult these directions referring to carburettion. In the absence of explicit directions the writer has found that the most reliable method of adjusting the carburetter is to examine the exhaust while the engine is running. That the several adjustments may bo properly made, the motor should bo started" the throttle opened In soiling the lover onohalf the distance on its sector, and the spark retarded. The Row of petrol should now be cut off by screwing down on the needle valve until the engine begins to miss fire. Having found this point where the minimum amount of fuel is fed to the carburetter, the petrol feed should be gradually increased by opening the needle valve, until the motor picks up and reaches its highest speed. Having determined the point where the motor runs at its maximum speed, the lock nut of the needle valvo should be sere-\\ ed tightly down m that the adjustment may not be disturbed. Having completed the adjustment of the petrol feed, the air valve should next be adjusted with advanced spark until the motor runs at its highest speed and the ignition is regular and constant Pay no attention to the blue smoke from the exhaust, as this is due solely to an excess of the lubricating oil and has no connection with the fuel supply system. In those carburetters where the air supply is automatically regulated by the suction of the piston, the needle valve is the only part needing adjustment, and the gasoline feed should be regulated by the needle valve until no trace of black smoke or strong odour comes from the exhaust. The one principal point to be remembered is to keep the mixture aa lean as possible, and at the same time obtain the full power of the motor. This is the best manner of obtaining the "best mixture" for any given motor, and the engine will not only be kept cooler and cleaner, but will run "more miles per gallon," and develop its full rated power. If everything is right, two turns of the handle ought to be enough for a start. If the engine remains after these, don't go on turning the handle, but look elsewhere for the fault. Carburetter starting' troubles

are mainly due to the following causes: petrol supply cock shut off (it occasionally jars in the off position) ; faulty mixture; stale fuel in float chamber ; strainer clogged with dirt; spraying nozzle clogged with grit ; water in petrol ; motor or carburetter cold; throttle valve loose on its spindle, or the level not advanced sufficiently on its section to admit a proper volume of gas to the cylinders. Accordingly, when the motor refuses to start, the first thing to do is to fill the float chamber with fresh petrol by priming the carburetter. Most cars are provided with a button or lever for this purpose, which raises the float valve from its seat, thus opening a passage for the fuel. After priming, the motor should start at the first few sharp up-pulls of the crank over compression, and if it does not, throw off the switch and look further for the cause of the trouble. If supply tank is empty, find out with a clean stick. If you think the pipe from the tank to carburetter is obstructed, open the drain cock below the float chamber to sco the flow of the petrol. If the stream is abundant and steady, all right. If the pipe is evidently clogged, unscrew the unions at each end of the pipe and do some cleaning with a bit of wire If that is not what is the matter, see if the fine brass mesh of the carburetter is at fault, for it nuicklv gets clogged. All other thino-s failing, examine the carburetter itself. The float sometimes may be at fault, especially if. being metal, it is punctured, or cork if it be sodden. Losing its buoyancy, it ceases to act, and the result is. misfire and refusal to start If punctured, mond with a light soldering iron; iP sodden, got ;i new cork. Sometimes the spraying nozzle is at fault Tn that case flooding the carburettor is sometimes very effective. It may be that, a wire pushed into the nozzle opening will remedy the evil. At high speeds the suction is likely to draw dust into the nozzle and choke it. It is sometimes possible to remove the obstruction by racing the engine and closing up the auxiliary air inlet valve, which Avill create a vacuum often sufficient to Mick the obstruction through the opening. Tf this fails to clear the orifico, a fine wire will solve the trouble. The height of the spravinsr nozzle is important, and the driver should not be too hasty in altering its position in the mixing chamber. If the nozzle is placed too high, the petrol level will be lowered considerably, relatively, that is>, and while enough fuel will be secured at high speeds (owing to the greater suction), the suction at low speeds will be insufficient to draw up the proper quantity of fuel. This will result in loss of power and the motor will frequently misfire. On the other hand, if the nozzle is placed too low, the petrol level will be raised unduly, and the carburettor will have a marked tendency to flood. The happy medium should be found by experiment, and once the level is adjusted to draw up the required amount of gasoline at both low and high speeds, the nozzle should not be disturbed again.