(2) If advance is insufficient during steps c
c. If dwell reading varies more than 2 degrees
and d, an excessively strong advance
(see NOTE below) from 0 to 20 inches of
vacuum, it indicates worn breaker plate
spring is indicated.
(3) If advance is insufficient in step c and
bushings and bearings or intermittent dis-
excessive in step d, or is erratic in
distributor wiring. The strands of wire
both steps c and d, distributor plate
may be broken within the insulation due to
is sticking or binding. Refer to
manual for proper service
d. Adjust vacuum control to zero vacuum.
This specification applies only to
For Delco-Remy breaker plate
distributors which have centrally lo-
spring tension test, see next para-
(On Auto-Lite distributors, Models IAT, IBP and
BREAKER PLATE SPRING TENSION TEST FOR
IBR which have side pivoted breaker plates, the
DELCO-REMY CENTER-BEARING BREAKER
dwell will normally vary by more than 2 degrees
when the vacuum unit is operated. No definite
specifications are given by the manufacturer for
This test is made to determine if the breaker
the dwell variation of these distributors since the
plate is free to rotate as it should under the
amount of dwell variation varies with the individ-
influence of the vacuum spark control unit. Ex-
ual distributor depending upon the amount of
cessive plate tension may cause sluggish action
maximum vacuum advance.)
of the advance mechanism, causing erratic tim-
ing under changing loads.
VACUUM SPARK ADVANCE TEST.
a. Remove the vacuum spark control unit
from the distributor. Finger tighten the
The vacuum spark advance adjusts the spark
small screw in the plate to provide an
timing according to the load on the engine to
attaching point for the spring tension scale.
provide peak fuel economy at moderate loads and
b. With the plate adjusted to full retard po-
full power without detonation at heavier loads.
sition (full travel in the direction of cam
In the course of the test look for improper cal-
rotation) hook the spring tension scale on
ibration, sticky or erratic breaker plate action,
the screw securely and pull, noting the
amount of pull necessary to start move-
the condenser with action of the plate. Refer
ment of the breaker plate.
a . Adjust speed control to 1000 rpm.
(1) This specification is not over 20 ounces
for the type ``A" plate shown, and not
b. With no vacuum applied to the unit (hose
over 15 ounces for the type "B" plate.
pinched) set the zero of the degree indi-
(2) Tension may be adjusted on type ``A"
cator ring in line with one of the arrows.
by adding or removing shim washers to
c. Open hose clip and adjust vacuum control
the tension spring on the underside of
to apply proper amount of vacuum for each
the plate and on the type ``B", by
specified check point in turn and note the
stretching or replacing the helical
amount of advance obtained. Compare with
plate tension spring.
d. Momentarily exceed highest vacuum value
specified, then reduce vacuum and again
SINGLE VACUUM CHAMBER LOADOMATIC
note advance obtained at each specified
With the exception of the advance mechanisms,
(1) If advance is excessive during steps c
loadomatic distributors are tested in the same
and d, a weak vacuum advance spring is
manner as described in the preceding pages.