CLAS B.LINE AC 0550BL Mode D'emploi page 16

HU 0014BL
7. Slightly lower than normal
reading, including when the throttle
is suddenly opened and then
released. DIAGNOSIS: Worn piston
rings. Perform a compression test.
3. Ignition system vacuum advance
On standard point systems and some electronic
ignition systems, two types of advance methods
are used, both of which must work properly
to achieve maximum performance and fuel
economy.
The fi rst method is mechanical or centrifugal,
which works by using weights located at the base
of the distributor. The masses move outward,
advancing the ignition timing as engine speed
increases.
The second method is vacuum advance, which
senses the engine load by means of manifold
vacuum. A vacuum diaphragm is mounted on
the distributor and connected to a rotating
internal base plate that advances or retards the
timing as required to accommodate diff erent
engine loads.
To check the correct operation of this system, always with the timing light connected, the
engine speed must be increased and the timing advance checked against the manufacturer's
specifi cations. If the vacuum advance does not work, remove the vacuum diaphragm from
the valve advance mechanism. Connect the product (fi g.3) and create a vacuum of 5-10 inHg,
controlling the dispensing at the same time. If a time advance is found, this confi rms that the
vacuum diaphragm and mechanical connections are in order and that the fault is a vacuum
supply. To confi rm this, connect the product to the vacuum supply line and check the gauge
reading. No vacuum should be noted at idle, but when the engine speed is increased, an
increase in vacuum should be observed. If this does not occur, reassemble the vacuum line
and check for restrictions or breaks.
METAL TRANSFER PUMP
8. Steady drop between normal
reading and low reading.
DIAGNOSIS: Burnt valve.
9. Normal at fi rst, but drops rapidly
when rpm is maintained at 3000
rpm. DIAGNOSIS: Restriction in the
exhaust system.