Vacuum Advance, Checking

Vacuum advance, checking

Work sequence





- connect SIEMENS 451 tester or equivalent, or tach and timing light according to manufacturer's instructions
- connect vacuum tester between throttle valve housing and vacuum advance unit connection
- set vacuum tester to allow vacuum to pass through
- start engine and run at idle
manual: 800 - 950 rpm
automatic: 850 - 1000 rpm

- if using SIEMENS tester or equivalent, read off indicated advance angle (basic angle) and note
- if using timing light, flash scale and note advance angle (basic angle)
- increase engine speed until reading on vacuum tester is higher than 266 mbar (200 mm Hg)
- switch vacuum tester so that it holds vacuum on side connected to vacuum unit
- leave engine running at idle (adjust if necessary)
- reduce vacuum on vacuum tester to 266 mbar (200 mm Hg) or 107 - 147 mbar (80 - 110 mm Hg)
- note advance angles determine vacuum advance by subtracting basic advance angle from measured advance angle

Example: last advance angle measured (-) minus basic advance angle (=) vacuum advance

- compare vacuum advance angles with specified values on