Have you put a spring on it? Because the spring is there to prevent hunting of the governor so if you haven't replaced that it could be your problem.
This is wrong. The whole purpose of a governor system is to maintain a steady desired rpm. They are intentionally designed to hunt for the selected desired speed.
Sounds like someone needs a lesson of governor operations. The spring pulls the governor toward full throttle position and mechanical governor pushes the governor arm toward idle. It is a balancing act and as you throttle up the spring applies more tension on governor arm as to overcome the governor trying slow down the engine. Without the governor spring with proper working governor the engine would only idle.
With a Briggs and many other engines with mechanical governors the first thing you do when you have hunting is to hold the throttle vane steady to see if the engine runs steady or starts to die or accelerates. If it stays steady then you check the static governor adjustment; otherwise, it more likely a fuel delivery problem or air leak.
The reason a static adjustment is indicated by surging if not fuel related is the play between the governor push pin and governor cross shaft arm. You are wanting zero clearance between these two parts. Governor flyweights pivots do wear out so it can come a time that governor will need replacing even when static adjustment is correct.
Governor spring rates are chosen for particular sensitivity with lighter spring rates typically usually used on generators where minimum rpms variance from unloaded to loaded (smaller Governor Droop) is critical for output Hertz to be stable.
