ENGINE WILL NOT START
When the engine will not start on cranking it eight times or so, it is useless to continue to crank it, for there is every reason to believe that something is wrong. Too often the difficulty is in forgetting to switch on the ignition circuit or to open the gasoline feed. Cranking the engine slowly will not reduce the pressure in the inlet pipe sufficiently to draw out of the spray nozzle the quantity of gasoline required to form an inflammable mixture; quick cranking is necessary. Too much priming will result in the formation of a rich mixture; the gasoline should be permitted to evaporate, or the carburetor drained, and then primed gently.
The failure of an engine to start on a cold day may be due to the slowness with which gasoline evaporates when chilled. As it is obviously most unwise to heat the carburetor with a flame, the best thing to do in such a case is to pack it with cloths soaked with hot water. A little gasoline squirted into the air inlet, or cotton waste soaked with gasoline and held over the same opening, will almost always permit the engine to be started; another method is to squirt a few drops of gasoline into the cylinders through the relief cocks.
ENGINE DOES NOT DELIVER FULL POWER
Regularly occurring explosions indicate that the cylinders are receiving the proper quantity of mixture, and that the ignition is operating correctly. If under these conditions the engine fails to deliver full power, which is shown by the sluggish running of the car, the trouble may be identified as the result of a condition by which power is absorbed between the engine and wheels. This may be from a slipping clutch, binding brakes, or tight bearings, these more probably on the wheels than on the change-speed mechanism or drive.
The brake rods may get out of adjustment, or the spring stick, with the result that the bands or shoes are in continual contact with the drums. A simple test for the condition of the brakes is to push the car across the floor by hand; it is not difficult to recognize unusual stiffness. This test also applies to the wheel bearings. Engine or transmission bearings that are too tight will heat, and a touch of the hand will show the presence of this condition. A tight bearing should be permitted to cool before readjusting it and proceeding.
WEAK EXPLOSIONS
Regular but weak explosions may be due to too rich or too poor a mixture, or to the escape of compression. Cranking the engine twice will produce a compression stroke in each of the four cylinders, and if there is a leak, the ease with which the piston in which it occurs may be pulled over dead center will show its presence. A little soapy water around the spark plug, relief cock, or other opening into the combustion space will show the escape of compression in the formation of bubbles. A hiss inside of the cylinder indicates a leaky piston ring, or that the openings of the rings are in line, and when this sound is sharp and clear, the presence of a broken ring. An additional proof of this is the undue heating of the crank case. If the compression is correct, the carburetor may be readjusted to improve the quality of the mixture. A poor mixture may be due to the partial clogging of the spray nozzle or its passages, and a rich mixture to the choking of the air inlet by dirt or dust, this being especially liable to occur when the part is oily.
MISSING EXPLOSIONS
The missing of explosions is a common failing of automobile engines, and while it may be due to a variety of causes, the most usual is that the spark does not pass. It is not always an easy matter to determine which of the cylinders is missing; if the missing is constant, the coolness of the exhaust pipe of one as compared to the others locates the fault. If the missing is not constant, the difference in temperature will not be noticeable, but the one at fault may be located by holding down all of the vibrators but one. If the cylinder corresponding to the free vibrator runs steadily, its vibrator may be held down and another released, this being continued until the faulty cylinder is located. The condition of the secondary circuit of this cylinder may be ascertained by disconnecting the secondary wire from the plug, and holding it about a half inch away from the plug terminal while the engine is cranked. If no spark passes when the timer makes contact, the trouble is in either the wire or the coil; if a spark shows, it should be of good strength, for a current that will produce a fair spark in the open may not have sufficient strength to produce a like result when under compression. If a good spark shows, the spark plug may be suspected of being fouled and thus short-circuited, of having a breakdown in its insulation, or of there being too great a distance between its points. The threads wear a little each time that a spark plug is removed from the cylinder, and in order to retain a gas-tight joint it is best not to unscrew the plug unless it is necessary.