kohler 23cw running rough

I have a 23 hp kohler that runs fine for a short time,then starts to rev up and down.If i put it on half choke,it sounds good again,,,I have put a new fuel filter on,new plugs,and a brand new carb.
I checked the fuel pump also,,puts out good
It is on a Derby zt2354,,,,,,,any ideas would be greatly appreciated

kohler 23cw running rough