How to adjust the RPM on a lawn mower. This mower was running a little slow at 2700 rpm. This video shows how to adjust the set engine speed. NOTE: I adjusted to 3150 rpm on the video. Later I dialed it back to 3000 rpm. 3150 sounded a little fast and the self propelled wheels were spinning a little to fast for me to keep up with. Use a tach to set the speed. Over-revving the engine can damage the engine or create a dangerous situation it the blade strikes a rock or comes loose.