As far as I know their carbs CANNOT HANDLE PUMP GAS. They will fail quickly and rebuilding will not work any longer than the original carb.
I agree, but that is true of so many small engines these days - not just Briggs & Stratton. The emissions-friendly carburetors are mostly to blame - the ones made of plastic with molded-in jets and idle air bleed circuits, no adjustment possible. No chokes, either - only primer bulbs. Just the damned primer bulbs are killed in short order by ethanol, even if the other parts were impervious you'd still have to replace that annually.
Notice too, how the manufacturers got smart and changed engine designs to prevent users from swapping in the older design carburetors.