Check for good fuel flow to the carb. If it doesn't flow, start checking the fuel line from the tank to the carb. You might have crud plugging the line and/or any fuel filters. I would guess since it dies about the same amount of run time after sitting, the float bowl is getting starved. The time spend sitting is enough to refill the float bowl again.
Others might tell you to check spark right after it dies which would be fine too. But based on what you said I'd personally look at the fuel system. To each their own!