Kohler carb issues ???

So all of a sudden my Husky lawn mower idles up & down , it races up then sounds like its going to shut off then up again & down again .... When I open it up its ok but when I throttle down it does this up & down idle thing .......Kohler engine , 24 hp ... SV725 ...... any thoughts

Your engine is surging.
GOVERNED engines surge because the air:fuel ratio is not strong enough to sustain wide open throttle.
Two causes
1) not enough fuel
2) too much air entering after the carb.

OK Last first,
Start the engine soak the area between the carb and the engine with WD 40 or similar goo from a TRIGGER PACK not a spray can unless you think singed eyebrows look sexy.

Not enough fuel
Pull the fuel line off the carb, put a bowl under it & get some one to crank the engine.
Flow should be strong, if not go backwards towards the tank looking for obstruction.

If flow was good remove carb and clean it out .