If the Yard Machines self-propelled lawn mower is not moving at the correct speed it is most likely due to the belt slipping off of the pulley. Check the belt to make sure it is not damaged or worn, if it is then replace it. Otherwise, make sure the belt is correctly on the pulley so that the lawn mower will move at the correct speed that is selected.
You can find the model and serial numbers located on your Yard Machines push or self-propelled lawnmower on the deck, or on the rear door of rear discharge units.
NOTE: if you need a part for the small engine in your Yard Machines push or self-propelled lawnmower, there will be a separate model/serial number for the engine. Here are the small engines that are available in your Yard Machines push or self-propelled mower. Visit the page of the engine you have to find out where the model/serial number is located for your small engine model: