Take matters into your own hands and advance the timing until it does ping, then retard it a little at a time until it doesn't do it. Make sure you can hear it! Some exhause noise might hide it. Got any hils near you? A low RPM pull up a hill will expose detonation.
What you describe is the correct function of the choke on a 1969 Pontiac. Stinkin' tach or not.
