[Jazzjr]

I had the same Backfiring situation happened to me, when the engine came up to normal operating Temps. Recently installed a Modern Upper Plate w/Chinese Parts.

I first changed out the condenser, same problem it would backfire when it got Hot. Drilled out another hole in my Re pro Gas cap, no help.
I ordered another set of Points Echlin, installed them, solved My Backfire Problem. Took the first set of Points Reinstalled them, to make sure that was the problem, started backfiring again, removed the Chinese points and Garbaged them.