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It is common for the EPA style breather in the fuel fill cap (or located within the tank) to get clogged. When you run the mower, fuel flows to the carb until a vacuum is formed... at which time the fuel can't flow and so the engine runs out of fuel. Without doing a thing, air SLOWLY comes back into the tank over the next several hours and then everything seems fine... until it happens all over.
Most of the time, a burst of air from a compressed air blower nozzle will break it free. Sometimes a squirt of "carb cleaner" helps. It's simply old, scuzzy fuel caught in the overly-complicated, EPA mandated breather.
>> Don't leave fuel in the tank over winter.
>> Try running a cleaner-stabilizer, like StarTron all year round.
>> To diagnose, unscrew the fuel cap (even 1/4 turn) and the issue will be cured immediately.