Worn or damaged tines, broken tine shaft clevis pins, a worn drive belt, a faulty transmission, a problem with the clutch cable, improper depth-stake setting or bad soil conditions can cause a tiller to do a poor job turning the soil.
The soil must be moist enough that it forms a ball when you squeeze it in your hand, but dry enough that the ball falls apart when dropped. Check soil conditions and water the area that you're tilling if the ground is too dry. Let the ground dry out if soil is too wet.
Check the depth stake setting and adjust it for the type of soil you're cultivating. Lower the depth stake to till at a 1-inch depth when using the tiller on soil for the first time or when breaking up hard soil. Also use the 1-inch depth setting to break up sod for shallow cultivation. Raise the depth stake to till loose soil and for deep cultivation.
Check the condition of the tiller tines and replace worn or damaged tines.
If tines don't rotate when the tine shaft turns during tilling, check the tine shaft clevis pins. The clevis pins are shear pins that connect the tines to the rotating tine shaft. The clevis pins are designed to shear off if the tines hit a fixed object during cultivation to prevent damage to the engine and other tiller components. Replace any broken tine shaft clevis pins.
If the tiller doesn't move and the tines don't spin when you pull the bail arm up against the handle, adjust the clutch cable to spin the drive belt when you pull the bail arm up. Replace the clutch cable if it's damaged. Replace the drive belt if it's worn or broken.
If the drive belt spins the transmission pulley but the transmission pulley won't move the wheels or the tines, replace the transmission.