10 hp briggs runs at high speed, govenor don't seem to be working

One possible cause for this problem is debris,sticking,or frozen linkage between the governor and the throttle butterfly. Depending on the make and model of your engine it will either be a mechanical governor that has a arm that goes down into the case or a air vane governor that is behind the recoil shroud of the engine. Move all the linkage that connects between the governor and throttle and speed lever to make sure it doesn't bind or sticks. If it does pray a little silicone or wd 40 spray on it to help reduce friction. Also on air vane governors they can become stuck from debris that inhibits it from moving make sure there is nothing in the way of the governor. If all of the linkage is working properly and you still have the issue try adjusting the the fuel mix screws and the high rev. settings on the throttle lever (if equip.).