Some tanks have a filter in the stem coming out. If that is plugged, fuel flow will be comprimised. or if a leaf or debris pushes op against it it to can reduce fuel flow. It's always a good idea to clean out the fuel tank and make sure you have good fuel flow.
Another possibility is a coil on it's way out. If it starts , once warm it dies it could be a coil problem. Put a spark tester between the spark plug and the coil wire and see if the spark is reduced in power or consistency.
If neither is your problem, take the carb apart and check the main jets opening. Unleaded gas after 3months time degrades and will clode the openings in the carbs jets and veigns. you can use a torch-tip wire cleaner to open up the opening in the main jet. I hope this helps
