Well it is still surging so either the carb is not supplying enough fuel or there is an air leak between the carb & the inlet valve.
On those B & S engines the O ring the carb bolts up to wears, goes hard or just leaks
The manifold it sits on has a tendency to crack on the under side where yo can not see it and on rare occasions the screws can come loose or the gasket fail
I replace about 15 to 20 of the manifold tubes annually and that reminds to add some to my pre-season order
Other than that the long pick up tube that goes into the fuel tank can split lengthwise or where it enters the carb body
It also has a screen that is subject to clogging
The diaphragm & gasket under the carb have a finite life and they are easily displaced unless you assemble the tank to the carb upside down ( Drop the tank onto the carb )
The main jet under the slip of mesh screen rarely clogs but it should be checked
When assembled the actual torque on the 5 screws is not all that important, but they must be all the same or the gasket will leak.
When it was apart the top of the tank must be checked for flatness as it is prone to warping .
