It sounds like the bad gasoline may have varnished the carb on that motor. You could add a carburetor and injector cleaner to the gasoline, or disassemble the air cleaner and spray carb cleaner into the throat of the carb when running. I am kind of partial to Sea Foam Motor Treatment (great in motorcycles). Also, might be worthwhile to pull the spark-plug and see if it is fouled. Also be sure the air filter is clean or replaced.
These are all standard maintenance items, and will make your machine run better.
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