Guardian 4389 Repair Manual page 110

SECTION 4.4
DIAGNOSTIC TESTS
RESULTS:
1. If INFINITY was NOT measured in Step 4, repair or
replace shorted ground Wire 18 between the J1 con-
nector from the circuit board to the stud or bullet con-
nector.
2. If INFINITY was NOT measured in Step 6 during crank-
ing, replace the circuit board and retest for spark.
3. If ignition spark still has not occurred, proceed to
Test 59.
TEST 59 - CHECK AND ADJUST IGNITION
MAGNETOS
DISCUSSION:
In Test 55, a spark tester was used to check for
engine ignition. If sparking or weak spark occurred,
one possible cause might be the ignition magneto(s).
This test consists of adjusting the air gap between the
ignition magneto(s) and the flywheel. The flywheel
and flywheel key will also be checked during this test.
PROCEDURE:
Note: The air gap between the ignition magneto
and the flywheel on single cylinder engines is
non-adjustable. Proceed directly to Steps 15,16
and 17 for single cylinder engines. For V-twin
engines, proceed as follows.
1. See Figure 23. Rotate the flywheel until the magnet is
under the module (armature) laminations.
2. Place a 0.008-0.012 inch (0.20-0.30mm) thickness
gauge between the flywheel magnet and the module
laminations.
3. Loosen the mounting screws and let the magnet pull the
magneto down against the thickness gauge.
4. Tighten both mounting screws.
Figure 23. Setting Ignition Magneto (Armature)
Air Gap
Page 108
PART 4
5. To remove the thickness gauge, rotate the flywheel.
6. Repeat the above procedure for the second magneto.
7. Repeat Test 55 and check for spark across the spark
tester gap.
8. If air gap was not out of adjustment, test ground wires.
9. Set the VOM to the diode test position. The meter will
display forward voltage drop across the diode. If the
voltage drop is less than 0.7 volts, the meter will "Beep"
once as well as display the voltage drop. A continuous
tone indicates CONTINUITY (shorted diode). An incom-
plete circuit (open diode) will be displayed as "OL".
10.Disconnect the engine wire harness from the ignition
magnetos and stud connector (Figure 24).
DIODE
SPARK PLUG
DIODE
SPARK PLUG
Figure 24. Engine Ground Harness
SWITCH ON TURNED OFF
Engine Runs Only One Cylinder
(Both Cylinders) Shuts Off
Won't Run
(No Spark)
Engine Runs Engine Won't
(Both Cylinders) Shut Off
Figure 25. Diode Failure Diagnosis
11.Connect the positive (+) test lead to Connector "A" (as
shown in Figure 26). Connect the negative (-) test lead
to Connector "B".
a. If meter "Beeps" once and displays voltage
drop, then the diode is good.
b. If the meter makes a continuous tone, the diode
is bad (shorted) and the harness must be
replaced.
c. If the meter displays "OL", the diode is defective
(open) and the harness must be replaced.
DC CONTROL
WIRE 18 TO
CIRCUIT BOARD
ENGINE
WIRE
HARNESS
CAUSE
1 Open Diode
2 Closed Diodes
2 Open Diodes