If your Ariens riding tractor is only moving at a slow pace even if you move the motion control lever to a faster position it is most likely because the belt is not on correctly.
There should only be about a half of an inch in play if the belt is on correctly, if you have more than that then check your manual for the belt pattern.
Once you have the belt on the correct routing pattern the tractor should move at the correct speed selected.
You can find the model and serial numbers located on your Ariens riding tractor on either the front right or front left side of the frame. If you don’t see them there, look at the dash support on the right side.
The model number for your Ariens tractor will be 6 digits long and start with a "9".
NOTE: if you need a part for the small engine in your Ariens lawn tractor, there will be a separate model/serial number for the engine. Here are the small engines that are available in your Ariens tractor. Visit the page of the engine you have to find out where the model/serial number is located for your small engine model: