not getting enough gas due to a couple things.
1 the filter has some stuff in it and blocking the gas that your engine needs when you bring up the throttle.
2 sticking float within the carb same idea the float is not going up enough to allow more fuel again to run the engine at a higher rpm those are the 2 things i'd check
Where is the location of the idle screw on the Briggs and Stratton 6.0 engine mulcher mower?
mower carbs built since around the mid nineties are non adjustable, except for idle speed,
Dirt in the carb or carb out of adjustment or both.
Top no-load speed is 3050 rpm.
It could have a pin hole in the petrol diaphragm
It may not be your throttle cable it might be that your governor is stuck.
The idle on a Toro push mower can be adjusted by turning the screw located on the carburetor. Turn the screw to the right to gain idle speed and turn the screw to the left to diminish idle speed.
The most common cause of engine surging (rev up and down) is a dirty air filter.
there should be a screw in the side of the carbuerator. turn the screw all the way in be careful not to bottom it out tight you will ruin the needle valve. then turn the screw opposite 1 1/4 times this should be good slow idle and also fast idle speed.
It is either an intake gasket leak or a head gasket.
A broken or maladjusted IAC valve.
Idle adjustment set to high