How does secondary air injection works in sudden de-acceleration?

WOW old school polution control.

When in decell on old school cars with Carborators specifically the fuel air mixture goes way rich and very small charges so the engine can't burn it properly.

To burn the left over fuel extra air is put into the exhaust manifold and this causes an after burn of the inside the manifold.

While some fuel injected cars were equiped with technology, fuel injection caused the end of the use of this junk. They shut the fuel off completely above 1100 to 1500 rpm removing the need.