Carbureted Models

Disconnect and check vacuum signal to vacuum advance hoses at vacuum advance unit. With engine running and coolant temperature below 140°F (60°C), check for vacuum at each hose. Vacuum should be present at both hoses.
If inner hose has no vacuum, check hose for leaks or other damage. If outer hose has no vacuum, check thermovalve for blockage and hose for leaks or other damage. If okay, replace thermovalve.
Reconnect vacuum hoses to vacuum advance unit. Allow engine to warm up fully (cooling fan comes on). Disconnect outer vacuum hose from vacuum advance unit. Check vacuum signal. No vacuum should be present. If vacuum is present, replace thermovalve and retest.
To view timing marks, remove rubber cap from inspection window on cylinder block by bellhousing. Connect timing light with timing advance capability. See Fig 1 . Disconnect and plug vacuum hoses at vacuum advance unit.
With engine at idle, turn advance control knob on timing light until White timing mark aligns with pointer. Read base ignition timing shown on timing advance meter. Timing should be as specified. See IGNITION TIMING table.

If timing is not as specified, loosen distributor hold-down bolt and adjust timing. Tighten bolt and recheck timing. Reconnect vacuum hoses to vacuum advance unit. Timing should advance to Red mark. If not, check vacuum advance diaphragm and distributor centrifugal advance mechanism.

Fig 1: Carbureted Timing Adjustment

Courtesy of AMERICAN HONDA MOTOR CO., INC.

IGNITION TIMING (Degrees BTDC @ RPM)

Application

Setting

Carbureted

Automatic Transmission ⁽²⁾

13-17 @ 700-750

Manual Transmission ⁽³⁾

18-22 @ 750-850

Fuel Injected

Automatic Transmission ⁽¹⁾

13-17 @ 700-800

Manual Transmission

13-17 @ 700-800

⁽¹⁾	Automatic transmission in Drive.

⁽²⁾	8-12 degrees BTDC on California vehicles.

⁽³⁾	13-17 degrees BTDC on California vehicles.