Honda lawnmowers come with a variety of different overhead cam (OHC) engines. Regardless of the engine model, all of the Honda OHC engines use the same process for idle adjustments. To adjust the idle, use the throttle stop screw and pilot screw. The throttle stop screw is found under the air cleaner assembly. The pilot screw is beside the carburettor. Adjusting a lawnmower's idle only takes a few minutes with the right tools.
Place the lawnmower on a level surface.
Start the lawnmower. Let it run until it gets up to operating temperature. This usually takes two or three minutes.
Push the throttle lever to the lowest setting.
Connect the tachometer to the spark plug wire.
Adjust the pilot screw with a flathead screwdriver until the engine runs at the highest revolutions per minute (RPM).
Turn the throttle stop screw with a flathead screwdriver until the tachometer reads 150 RPM. Turning the screw counterclockwise will lower the RPM and turning clockwise will raise them.