Possible causes of engine failure are many, and to save time and avoid
interference with standard adjustments the operator is recommended to
carry out a systematic search in locating the seat of the trouble. For
example, when an engine fails to start, stops suddenly or runs
·
unsatis
factorily, the cause can usually be found under one or more of three main
headings, ignition, fuel system or mechanical faults.
The following sequence has therefore been planned so that, knowing
the symptoms, location of the fault is simplified and its cure quickly
achieved.
ENGINE REFUSES
TO STA.RT
SUDDENLY
OR STOPS
Ignition
.
System
Check for spark at the plugs, while they are still in position, by short
circuiting the centre electrode of each plug, in turn, to the cylinder block;
use a wooden-handled screwdriver, w
h
ile an assistant turns the engine
fairly fast.
.
If no spark is obtained by this method, remove the plugs, examine the
condition of the electrodes and clean if necessary. If the plugs are wet,
determine whether from fuel, oil or water, and ·check for fuel or
mechanical fault as described later.
When the plugs are cleaned and adjusted, place them on their sides
on the cylinder head. with the leads attached and the electrodes exposed
to view. Re-check for spark by again turning the engine.
If no spark is obtained, or the spark is weak, change the plags
concerned.
If a good spark is now obtained, refit the plugs and see whether the
engine will start. If it refuses to start, check hack through the ignition
system as follows.
Check if switched on and test the leads to the switch, the earthing
terminal on the magneto, and the plug leads.
If the switch and leads are satisfactory, take off the distributor cover.
See that the contact gap width is correct
(0·012
in.), that the contact arm
moves freely on its pivot, that the electrodes in the cover are clean and that
the brush which is connected to the centre lead is free.
Fuel System
When a spark is obtained by short-circuiting the plugs, inability to
start the engine may be due to a blockage in the fuel system, in which case
make sure that fuel is available at the carburettor by opening the drain
cock (Fig.
10).
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