"Timing is set to 4 degrees ATDC at 800RPM with the vacuum advance hose in place. When I remove and cap the vacuum hose, the timing changes to 23 degrees BTDC at idle"
Do you understand what vac retard means? Look at your statement. You removed the vacuum and the timing advanced 27 degrees. That is called vacuum retard. With vacuum the timing is retarded from that which it is, without vacuum.
Bosch Master, ASE Master, L1
33 years MB technician