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180 the engine. This took a long time to discover. A slight leak of compression will also sometimes produce a squeak at each explosion.

Irregular.—Popping Noises in the Carburator or Induction Pipes.—These are minute and harmless explosions caused by:—

i. Induction valves opening too much, or

ii. Sticking, or

iii. Their springs being too weak.

iv. Cold ignition tubes.

v. Retarding the ignition suddenly at high speeds, or

vi. Bad carburation.

Bursting Noises (irregular} coming from the Engine.

i. These indicate:—Burst joint at valve cover, sparking plug, or ignition tube. Spare washers specially made must always be carried to rectify these.

ii. A platinum tube may have burst. Spare ones should always be carried. What to do if Ignition Tube bursts and you have no spare one. If you have no spare one, the hole of the old one should be closed up as much as possible with a small hammer, then replace the tube with the hole in such a position as not to blow out the burner or its neighbour. If you can keep the burners alight progress can thus be made. Failing this, the faulty tube or the hole leading to it must be blocked up, and the car run home on the remaining cylinder or cylinders.

iii. Loud Report in Exhaust.—This is due to several unexploded charges having collected in the silencer, and being ignited by the incandescent products of the next fired charge; switching the electric ignition off and on will often produce this, so may a sudden retarding of ignition, or a semi-cold platinum tube.

There is no danger in these explosions—startling as they seem—beyond the risk of splitting the exhaust box or pipe.