I have a 2006 Craftsman lawn tractor that is popping through the carb, this is new for the 20hp V twin Intek B&S 407577-0217-E1
It is called a 'backfire' and often means the timing is way off or an intake valve is not closing (could be a bad valve spring, valve seat, slipped cam timing,etc.).
Today I adjusted the valve clearance to the factory setting and the tractor worked fine.
How did the valve adjustment get off?
The two-cylinder Briggs engines with overhead valves are well known for needing periodic and rather frequent valve adjustment.
Sounds like it is time to add a jamb nut on the valve stud.