Timing Adjustments

By the numbers (proven method): set the mechanical advance to 32° BTDC at ~2600 RPM (timing tape helps — far more accurate than the cast marks). Then reconnect the vacuum advance and tune total advance to about 50° at cruise vacuum. To dial the vacuum advance: with a gauge in the car, note max vacuum at a steady 2500/3000/3500/4000 RPM on flat road; then at ~2600 RPM apply that vacuum to the advance and check for ~50° total (adjustable-advance distributors tune to it). If it spark-knocks, back off — knock usually means too much vacuum advance, too lean at max advance, or too-high compression for your fuel (don’t run more than ~9.5:1 on 93 octane).

By ear: advance the distributor until the engine just starts to miss, back off a little, then rev and listen for ping and retard slightly until the ping is gone or minimal. One caveat: timing set for the best idle is often too advanced to start easily — better to set the initial timing to what starts easily, then tune the distributor weights and springs so total advance comes in around 700–800 RPM. Verify with a timing light and write it down so you can reset it after pulling the distributor.