The stock distributor mechanism, produced by the tens of millions and as found in any pre-EFI engine since perhaps 1930, anticipates and compensates for engine ignition timing under a wide range of conditions.

The reason why "locked" appears to function reasonably:
1. No valid comparison made (the distributor was never correctly re-purposed).
2. Limited use ("it hardly gets warm").
3. Large initial spark lead more or less imitates much smaller (best) ignition lead + vacuum advance for light throttle, but:
a. It doesn't self-adjust for load conditions.
b. It's only close to what the engine requires, not exact.
c. WOT at low RPM will knock badly.

Typical distributor set-up:
1. Initial lead 15° (mild engine) to 20° (big cam). Anything else may be that strange off-idle carb problem...
2. Auto-advance curve shortened to total (known by best MPH) - initial lead.
3. Advance weight + light springs give full advance by 1,500 RPM.
4. Vacuum advance adds 20-25° degrees under high vacuum, drops out before power valve opens.