Fig. 75.—Ignition-tubes provided with needle valves to facilitate starting.
The mere enumeration of defects caused by leakage is sufficient to indicate the remedy to be adopted. It may be well to recall in this connection the important part played by the ignition-valve. If it be leaky, or if
its free operation be impeded, starting will always be difficult.
Electric Ignition by Battery or Magneto.—If the electric ignition apparatus, whatever may be the method by which the spark is produced, be imperfect in operation, the first step to be taken is to ascertain whether the spark is produced at the proper time, in other words, slightly after the dead center in the particular position given to the admission device at starting. If a coil and a battery be employed, it is advisable to remove the plug and to place it with its armature upon a well-polished metal surface to produce an electrical contact, preventing, however, the contact of the binding post with this metallic surface. The same method of inspection is adopted with the make-and-break apparatus of an electric magneto. In both cases it should be ascertained whether or not there is any short-circuiting. The contacts should be cleaned with a little benzine if they are covered with oil or caked grease.
If no spark is produced at the plug or at the make-and-break device it may be inferred that the wires are broken or that the generating apparatus is out of order. A careful examination will indicate what measures are to be taken to cure the defects.
Premature Ignition.—It has several times been stated that the moment of ignition of the gaseous mixture has a pronounced influence on the operation of gas-engines and upon their economy.
Premature ignition takes place when there is a violent
shock at the moment when the piston leaps from the rear dead center to the end of the compression stroke. The violent effects produced are all the more harmful because they tend to overheat the interior of the engine and thereby to increase in intensity.
Premature ignition may be due to several causes. If a valveless hot tube be employed it may happen that the incandescent zone is too near the base. If the tube be provided with a valve, it very frequently happens that the valve leaks or that it opens too soon. In the case of electric ignition, the circuit may be completed before the proper time, because of faulty regulation. The suggestions made in the preceding chapters indicate the method of remedying these defects.