[header] How to store a lawn mower [title] Run your mower out of fuel. [step] Condensation inside the fuel tank can seriously damage the mower's engine: if moisture develops, it can cause corrosion, clogs, and other problems. Having an empty tank before your mower is put into storage lowers the risk of condensation forming. 
Start up your mower, and let it run until it no longer starts back up, and the fuel lines are empty. [substeps] Keeping fuel inside the mower is also a fire hazard.