Thunderbolt Iv Ignition Timing - Mercury 305 CID Service Manual

Thunderbolt IV Ignition
Timing
1. Connect timing light (91-99379 or similar) to No.
1 spark plug. Connect power supply leads on
light to 12 volt battery. Refer to "Specifications"
for cylinder numbering and location.
2. Connect tachometer to engine.
3. Start engine and run at normal idle speed.
4. Aim timing light at timing tab, located on timing
gear cover and crankshaft torsional damper.
IMPORTANT: GM engine timing marks (on tab)
are in 2-degree increments. MCM and MIE LH en-
gines will have "A" (Advance) mark to the left of
"0." Timing must be set on the "A" side of "0"
(Top Dead Center).
a - Degree Marks
b - Timing Mark
Index
90-823225--1 1096
a
b
72328
72851
5. Adjust timing by loosening distributor clamp and
rotating distributor body as required until timing
mark on damper or pulley lines up with the mark
on tab specified in "Specifications." Tighten
clamp and recheck location of timing mark.
6. Stop engine and remove timing light.
THUNDERBOLT IV AND V IGNITION SYSTEM - 4B-13