Equus 3551 - INNOVA Inductive Timing Light (DIS) - Manual (Page 9)

Depending on make and model, a vehicle may
be equipped with a single timing control device,
or two or more devices may be used in
combination.
Checking Mechanical/Centrifugal Timing
Advance
1. Rotate the Advance Control Knob
counterclockwise to the "0" degree
position.
2. While performing an INITIAL (BASE)
TIMING CHECK as previously described,
slowly increase engine speed to the
manufacturer's specified rpm for
mechanical/centrifugal advance, and
observe the rotating timing mark for
change. The timing mark should appear to
move smoothly, in the opposite direction
of engine rotation, away from the
reference pointer.
3. Rotate the Advance Control Knob
clockwise until the rotating timing mark
and the reference pointer realign at the
base or initial timing mark as previously
recorded. Read the degrees of mech-
anical or centrifugal advance on the
Advance Control Knob's calibrated dial.
See Figure 7.
4. Note the degrees advance indicated by
the Advance Control Knob's calibrated
dial, and compare this value with the
manufacturer's specification for mech-
anical or centrifugal timing advance for the
rpm specified.
■ If the position of the rotating timing
mark does not change during the
mechanical/centrifugal advance
check, the mechanical weights
associated with your vehicle's
mechanical advance mechanism (if
equipped) may be rusted or binding.
5. Repeat the test, as needed, for all engine
speeds specified by the manufacturer's
instructions.
Checking Vacuum Timing Advance
1. With the engine off, disconnect the
vacuum hose from the distributor's
vacuum advance port. Plug the vacuum
hose securely.
2. Connect the vacuum pump to the
distributor's vacuum port. Do not apply
vacuum at this time.
3. Start the engine and perform INITIAL
(BASE) TIMING CHECK as previously
described. Record the degree(s) of initial
(base) timing.
7
NOTE
Advance timing test procedures vary widely
from vehicle to vehicle. The following
paragraphs provide general test procedures
for checking mechanical/ centrifugal advance
and vacuum advance. ALWAYS make sure
initial timing and dwell are correct before
checking advance timing. ALWAYS refer to
the service manual for the vehicle under test
to obtain the proper timing procedures and
specifications. OBSERVE ALL SAFETY
PRECAUTIONS.
0
5
10
15
20
25 30 35
40
45
50
55
60
TIMING
LIGHT
A D V A N C E
Fig. 7. Advance Control Knob Operation
NOTE
If timing mark movement is rough or erratic,
the mechanical advance system may be
defective. Service and repair the mechanical
advance system in accordance with the
manufacturer's instructions before continuing.
NOTE
A vacuum pump equipped with a vacuum
gauge is needed to check vacuum advance.