Norm,
It was timed with a timing light, then I checked the vacuum. The vacuum gage was connected to read manifold vacuum, not the distributor vacuum (the distributor port). The last time I ran it, after I rebuilt the carb, it does not pop while idling, occasionally while holding a steady rpm above 900 and constantly while the engine is slowing down. I have not taken it on the road to see how it acts under load; that's for this weekend.