Those rideon-size Briggs engines have gravity fuel feed. If the needle and seat does not seal, the float bowl floods, and the disharge nozzles in the venturi are lower than the top of the float bowl, so fuel runs into the venturi. It can't get high enough to go through the inlet valve into the cylinder, though, unless there is no overflow vent in the top of the float bowl. On the other hand it could go through the valve guide and get to the sump that way.
The short answer is, fix the needle and seat, and don't leave the fuel on.