A tiller motor can become seized after the engine has been in use for some time, even if you have attempted to keep the machine in good condition. A seized motor will cause your tiller to become completely inoperable. You can fix a seized tiller motor using engine release/anti-seize solution. Inserting this solution into the engine and freeing up the motor does not require previous tiller troubleshooting expertise.
Turn the tiller off.
Find the spark plug where it sits within the spark plug hole on the top of the tiller's motor. Pull the black ignition wire out of its rear as a safety precaution. Pull the spark plug out of the hole and set it aside.
Pour an engine release/anti-seizing liquid into the engine through the spark plug hole. The instructions on the bottle of your specific brand of engine release liquid will indicate how much you are supposed to pour into the engine.
Wait 24 hours as the liquid works through the engine. Do not attempt to run the tiller or troubleshoot it further during this time period.
Set the spark plug back into place within the engine's spark plug hole. Slide the ignition wire back into the spark plug's rear.
Start your tiller's motor. Several attempts may be required initially.