B Series Truck L4-2000 1998cc (1986)
Vacuum Advance Diaphragm: Testing and Inspection
1.
Warm up the engine fully.
2.
Make sure that the idling speed and ignition timing are within specifications.
IGNITION TIMING: 6° BTDC
IDLE SPEED: 800-850 rpm
Fig. 3 Centrifugal spark advace curve
3.
Remove the vacuum hose from the distributor vacuum control unit and plug the hose.
4.
While gradually increasing engine rpm, check changes in ignition timing with a timing light Fig. 3.
Excessive advance: Governor spring is fatigued (If the governor spring is broken, the initial advance is very quick and high).
Insufficient advance: Governor weight or cam is not operating properly.
