there is a lever associated with the choke. when the engine needs more power the choke moves to the closed position. There is a governor spring attached to the lever.
If this spring is shortened the choke will not be able to move back to full open. This is not recommended though. I did it last fall for the last cut of the year. Sparks were flying from the starter housing flywheel and I used two tanks of gas for a very small yard, normally I get by with about 3/4 of a tank. The mower sure was screaming though. This lever can usually be located by looking down between the starter housing and the air filter.
mower carbs built since around the mid nineties are non adjustable, except for idle speed,
Top no-load speed is 3050 rpm.
4.5 mower will start and run for two seconds
All Briggs engines run at 3000 rpm. Slacking off the 10mm nut on the gov lever adjusted the arm of the gov to which ever speed you whant but be careful not to over do it
Replace or change the tension on the spring on the manual control to throttle connection. Most speed problems are caused by the manual cable control cable being maladjusted and one cannot get a mower to run at a decent speed.
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 Poulan XT 30 In. Deck 12.5 HP Briggs & Stratton 6 Speed Tractor is inexpensive
That linkage is attached to the governor which is trying to keep the engine running at a constant speed. Most likely, the surging is caused by a dirty.clogged air filter.
The fuel control is adjusted to set idle and maximum speed.
governor not moving freely or dirty carb
My engine is idling too high. How do I adjust the idle speed?
The speed controls are programmed into the engine ECM. The only way to disable them is to have the ECM settings adjusted.