When an engine is stored with gas in the tank and carburetor, the gas evaporates and the oil remains.

That oil attracks dust and when fresh gas hits the tank, it gets diluted and adds to the oil content of the new fuel.
The oil deposits in the carburetor clog filters and disturb valves.

Spark plugs and carburetor are not happy with that extra dirt and oil.

That may be part of your problem.

Best luck with that!