1972 Cheyenne 350 Engine problem

[brown7373]

I am having a problem with my 350 Q-jet 4bbl. A few weeks ago, it seemed to start funny, almost made a pop sound. But it started, idled and seemed to run fine, until I tried a little harder acceleration. It was making some noise and lacked power. I have since decided it sounds like the engine is now pinging on any acceleration above gentle.

Water temp is okay and confirmed with infrared on the hoses, radiator, thermostat housing etc. which all read low 180, +-. Oil pressure also fine. It idles smooth, A/C runs fine and doesn't load up the engine. But even moderate acceleration, like to speed up a little from 50 mph and the engine pings. I have filled up several times from a couple different gas stations that I have regularly used. I have always used the 10% ethanol with no issues.

I just completed a 2 hour, 90 mile round trip, and other than pinging on acceleration, it was fine. Before this, in 14 years of ownership, it has NEVER pinged. 8:1 compression. I checked the timing when I got home, thinking maybe I jumped a tooth, but it was 6 degrees advanced, right where I have always kept it.

Any ideas what is wrong? 12K on plugs, Pertronix I. This did not happened gradually, it just suddenly started pinging.