If a magneto is fitted the earth connexion should be open, but if a coil and accumulator are fitted the earth connexion should be closed.
(b) Is the petrol reaching the carburettor jet?
Before removing the jet for the purpose of examining and cleaning it, it would be advisable to ascertain whether the petrol was reaching the float chamber. Provided there is a reasonable amount of petrol in the tank and the tap is turned on, there must be a stoppage either in the petrol filter, the petrol pipe, or the bottom portion of the float chamber. Examine the filter and float chamber before disconnecting any pipes.
(c) Is there a good compression in all the cylinders?
If there does not appear to be any compression in any of the cylinders, it is probable that the carburettor throttle is closed and no air or gas can enter the cylinders. If there is a good compression in some cylinders and a poor one or none at all in others then—
(1) One or more of the valves may be held off its seat by dirt, by distortion, or by some derangement of the valve gear. Examine the valve gear externally, turning the engine slowly to watch its action. Afterwards remove valve caps and inspect valves if necessary.
(2) One or more of the sparking plugs or valve caps may be short of its washer. In this case the blow will be heard as the engine is turned round by hand.
(3) A piston may be cracked or broken or a cylinder cracked.
(4) A cylinder may have got badly worn and the rings on the piston jammed so that they no longer keep it gas-tight.
(d) Is the engine very stiff to turn over?
Stiffness is due as a rule to lack of oil on the cylinder walls, caused by absence of oil in crankchamber or the film of oil on the cylinder walls having been washed off when priming the engine with petrol in attempting to start it. If a connecting rod is bent, or the crankshaft distorted or a piston ring broken, stiffness will also be noted. Very often by removing the valve caps and pouring a teaspoonful of oil or paraffin into each cylinder the engine may be freed by vigorously turning the starting handle by hand until the cylinders and pistons are well lubricated.
(e) Is there any sign of an attempt to fire the charge such as an occasional puff of smoke from the exhaust or inlet, or an occasional jerk round of the engine as you turn the starting handle, or an occasional “bang” in the exhaust box?
If the ignition is “on” and the carburettor jet clear, the compression good and the engine quite free, yet there is no sign of a “fire” from any of the cylinders, it is possible that air is leaking into the induction pipe through a faulty joint or any one of the following ignition troubles may have occurred:—