28Air inlet temperature control
check (carburettor models
only)
2
Refer to Chapter 4A for details.
29Fuel filter renewal
3
Fuel filters are fitted in various locations
throughout the range. Some may be ‘in-line’ in
the fuel tank itself, or fitted into the
carburettor.
Refer to Chapters 4A or 4B, as appropriate.
30Spark plug renewal (SOHC)
2
1The correct functioning of the spark plugs is
vital for the correct running and efficiency of
the engine. It is essential that the plugs fitted
are appropriate for the engine. Refer to the
specifications in Chapter 5. If this type is used
and the engine is in good condition, the spark
plugs should not need attention between
scheduled service replacement intervals.
Spark plug cleaning is rarely necessary and
should not be attempted unless specialised
equipment is available, as damage can easily
be caused to the firing ends.
2Identify each HT lead for position so that the
leads can be refitted to their correct cylinders.
Then disconnect the leads from the plugs by
pulling on the connectors, not the leads.
3Clean the area around each spark plug
using a small paintbrush, then using a plugspanner (preferably with a rubber insert),
unscrew and remove the plugs (see
illustration). Cover the spark plug holes with
a clean rag to prevent the ingress of any
foreign matter.
4The condition of the spark plugs will tell
much about the overall condition of the
engine.
5If the insulator nose of the spark plug is
clean and white, with no deposits, this is a
sign of a weak mixture, or too hot a plug (a hot
plug transfers heat away from the electrode
slowly -a cold plug transfers heat away
quickly).
6If the tip and insulator nose is covered with
hard black-looking deposits, then this is
indicative that the mixture is too rich. Should
the plug be black and oily, then it is likely that
the engine is fairly worn, as well as the mixture
being too rich.
7If the insulator nose is covered with light tan
to greyish brown deposits, then the mixture is
correct, and it is likely that the engine is in
good condition.
8The spark plug gap is of considerable
importance, because if it is either too large or
too small, the size of the spark and its
efficiency will be seriously impaired. The spark
plug gap should be set to the figure given in
the Specifications, in Chapter 5.
9To set it, measure the gap with a feeler
blade and then bend open, or close, the outer
plug electrode until the correct gap is
achieved. The centre electrode should never
be bent, as this may crack the insulation and
cause plug failure, if nothing worse (see
illustrations).10Before fitting new spark plugs check that
their threaded connector sleeves are tight.
11Screw in the plugs by hand, then tighten
them to the specified torque. Do not exceed
the torque figure.
12Push the HT leads firmly onto the spark
plugs, ensuring that they are connected to
their correct cylinders.
31Distributor cap and HT lead
check
3
1Remove the distributor cap and HT leads,
and wipe them clean.
2Also wipe clean the coil connections.
Remove the rotor arm, then visually check the
distributor cap, rotor arm and HT leads for
hairline cracks, and signs of arcing.
1•14Every 18 000 miles or 24 months
30.9A Tools required for spark plug
removal, gap adjustment and refitting30.9C Measuring the spark plug gap with
feeler blade30.9B Measuring the spark plug gap with
wire gauge
30.3 Removing a spark plugWarning: Before carrying out
the following operation, refer to
the precautions given in “Safety
first!” at the beginning of this
manual, and follow them implicitly. Petrol
is a highly dangerous and volatile liquid,
and the precautions necessary when
handling it cannot be overstressed.
It is very often difficult to insert spark
plugs into their holes without cross-
threading them. To avoid this, fit a
short length of 8 mm (internal
diameter), rubber hose over the end of
the spark plug. The flexible hose acts
as a universal joint to help align the
plug correctly. Should the plug begin to
cross-thread, the hose will slip on the
spark plug, preventing damage to the
thread in the cylinder head.
Number the HT leads before
removal to ensure correct
refitting.
