Sounds to me like it's time for a New Spark Plug.
Your chain saw sounds like it's having an overheating problem which to me indicates a bad Spark plug.
Here's a link to Check out the technical workings of a Spark plug... GOOD LUCK ..
NGK Spark Plug Tech Support
Democracy is two wolves and a lamb voting on what to have for lunch.
Liberty is a well-armed lamb contesting the outcome of the vote.