Chainsaw compression

Pull the muffler and inspect the piston. 
 
You likely have scoring to the piston and thus the cylinder wall.  
 
Getting over heated, lean running or straight fuel can cause the issue.
 
If the piston / cylinder looks fine, you'll need to pull the cylinder and
measure the piston ring end gap (for a worn ring(s).
 
 
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Please post back what you find..
 
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