Your engine should Idle around 1000 RPM, and run around 3600 RPM at full throttle... The governor is only going to attempt to hold the RPM setting you have chosen, if you are mowing at less than full throttle, that is what it will attempt to hold...
If you are at full throttle, it will hold that until it gets overloaded... You can reduce the overload by slowing down the forward speed, OR raising the deck, so it has less to cut...
If you are finding that you can not mow your grass as fast & as short as it once cut... You have something using up the power, OR your engine is not making the same power it previously made...
If the engine is not putting out the HP it once did... It could be from a lack of fuel flow or weak spark... Check the fuel lines & carb, for the first.
Check the spark Plugs and ignition for the other... :smile:KennyV