OK, AP squirter looks good.

The backfire events were a single POP at WOT (or close to it). I got it to happen 3 more times.
Each time I was cruising at 45-55 mph. When I stomped on the gas quickly the car would backfire. I would hear only one POP. I have a vacuum gage in the car, so I watched it after the first back fire. When I would rapidly stomp on the accelerator pedal the manifold vacuum dropped to 5 " Hg or below and the POP was heard. then I tried a deliberate but slower acceleration and I could get to 5 Hg without a POP. I didn't note the rpms, I'll have test it again to get to back on that.