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.
If the secondary circuit is proven to be in good condition, attention should be paid to the carburetor, for a poor mixture, or water in the gasoline, will cause the engine to miss. A badly fitting exhaust valve will permit the burned gases to be drawn back into the cylinder, the fresh charge thus being weakened, and as the valve will shift around on its seat, this may happen irregularly. Missing will also be caused by a weak or broken inlet-valve spring, or by the sticking of the inlet valve, these conditions resulting in failure to retain the mixture in the combustion space during the compression stroke. This pushing back into the inlet pipe of the charge will usually produce a popping or gurgling noise that is easily recognized.