Backfire in overrun mode (load change)

[DRG-ler]

Hi folks, a few days / weeks ago I noticed "new" appearances of my 30s Tudor.

My manifold gaskets were burned as a result of a warped manifold, and the last time I drove this manifold I had backfiring in the exhaust (when accelerating ...). Because of the faulty seal at the time, the whole thing was so uncomfortable that I had always stepped on the gas on the way home.

Now I've got a new manifold. This was completely redesigned and planned together with the intake manifold by the engine manufacturer. The whole thing installed with new seals, runs great! I also installed a seal for the rear silencer for the first time. Until then, this was backsing.

I sealed the carburetor flange with Hylomar sealing paste due to the lack of a paper seal. Should also be tight.

Regardless of all the new / restored seals, the "backfires" have unfortunately remained.
It is now not a loud popping, but more like the turbo brawl of modern cars of higher performance classes. However, I would be interested to know where this comes from and whether / how it could be eliminated.

As such, the engine runs super and quietly, pulls through occasionally, and gives no cause for complaint.

Who has tips?

Greetings Andy.