Page 10For technical questions, please call 1-800-444-3353.SKU 40963
Testing Vacuum Advance
Speed the engine up slowly to the 1.
manufacturer’s specied speed for
this test (often 2000 RPM) and leave
the vacuum line detached from the
distributor.
Aim the Timing Light at the timing 2.
marks and turn the timing advance
knob on the back of the timing light
up slowly until the timing mark moves
to TDC or 0.
Connect the vacuum line to the 3.
distributor.
If the timing mark stays still, the 4.
trouble could be a plugged line,
a leaky diaphragm, or a frozen
distributor plate. See a certied
mechanic if the mark doesn’t move.
Read the amount of vacuum advance 5.
from the timing marks on the engine.
Compare with vehicle service
manual.
Checking Distributor Cam Wear
This test is done after the timing has 1.
been set and the timing light lines up
with the reference pointer for cylinder
number 1.
#1 Cylinder
Opposite
Cylinder
8 Cylinder
3 1
6 2
5
4
7
8
Opposite
Cylinder
#1 Cylinder
6 Cylinder
16
4
3
2
5
#1 Cylinder
Opposite
Cylinder
4 Cylinder
2
3
1
4
Note: The opposite cylinder is opposite
the #1 Cylinder on Distributor Cap.
FIGURE 3
2. Connect the Timing Light to the
spark plug wire directly opposite (180
degrees) from the number 1 cylinder
on the distributor cap.
(See FIGURE 3)
Start the engine and aim the Timing 3.
Light towards the timing mark. The
reading should be the same as when
the Timing Light was connected to
the number 1 cylinder wire. If not,
the probable cause is a worn out
distributor cam, bushing, or bearing,
or bent distributor shaft. Contact
a qualied service technician for
repairs.
REV 07h, 09g
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