Try servicing the air filter.
Looking down the list of different kinds of portable generators from Briggs and Stratton, most of them are 4 star and up, so yes, I think you can say that it is a high quality generator.
Loosen the carborator and let the gas out, or just let it cool down
The most common cause of engine surging (rev up and down) is a dirty air filter.
They did not they bought Murray and have since closed it down. Most all B & S stuff is now made in China.
Dirt in the carb or carb out of adjustment or both.
The most comon cause of an engine that keeps revving up and down (aka surging) is a dirty air filter.
Leak down test : Uses 70lbs pressure to test for leaks around valves and cylinders.
one reason for this is the air inlet on the petrol cap is blocked or too small causing a vacuum in the petrol tank and starving the motor.
You may have clogged jet in the carb, or in the small fuel filter. Check everything from the tank down to carb, and if necessary take carb apart.
Carburetor adjustment or if unattainable rebuild the carb. about $20 and 1/2 hr Before you start messing with the carburetor, check the air and fuel filters.
front right of engine, from driver seat perspective, follow the 1/4 inch spark cable down to where plug is