The 1 most common part(s) or condition(s) which cause the symptom Lawn mower overheats are listed below starting with the most likely. Check or test each item and watch any available videos.
If the engine overheats check for clogged cooling fins. All air-cooled small engines have cooling fins manufactured right into the engine's cylinder head and short block. These fins help to dissipate the heat from the engine. If the fins get clogged with dead grass, leaves or other debris they won't allow the engine to cool properly and it will overheat.