Small Engines (Lawn Mowers, etc.): Chain saw w/ no power at high end, air mixture, exhaust port

Question
Hello!

I have a 42cc Sears chain saw (358.350870)that runs and can be used except that at high end, it lacks power. I consequently have to back off on the pressure to let it catch up and then continue cutting. I have checked the spark plug, cleaned the fuel filter and have run carb cleaner through it. I also changed the gas. Nothing helps plus it may be getting worse! It starts well and runs fine and it will rev good without a load on it.

Any suggestions for me?

Thanks for your help.

Answer
Hello Doug:

Try Setting the Carburetor Air Mixture Screws. The Following is the Instruction File for Setting the Air Mixture Screws. Any Input is Appreciated. The Procedure is the Same for 1 or 2 Mixture Screws, Just Use the Instruction File and Skip Over the Section with the Missing Mixture Screw. Now Setting the Air Mixture Screws:  ****Turn the Idle Air (L) and Main Air (H) Mixture Screws In Until SNUG **Do Not Jam** Then Reverse Both Screws 1 1/2 Turns. Set the Throttle Full Open, Start the Engine. Turn the Main Air (H) Mixture Screw Clockwise Until Proper Revs are Obtained. (On Mower Engines: Use your Finger to Push the Governor Arm and Rev the Engine while Setting the (H) Air Mixture Screw. On Chainsaws and Trimmers Use the Trigger to Rev the Engine Up Until the Proper Revs are Achieved) Occasionally you May have to Turn this Counter Clockwise to Achieve the Proper Revs. Now Allow the Engine to Idle. Set the Engine Idle Screw (Not Idle Air) so the Engine will Stay Running if Required. Now Set the Idle Air (L) Mixture Screw so there is No Hesitation when Throttling from Idle to Full Throttle. Reset the Engine Idle if Required.**** If you Still Lose Power at (H) Full RPMs, then the Exhaust Port or Muffler May be Restricted and Require Cleaning or the Carburetor Requires Soaking and Cleaning. If Either (the Exhaust Port or Muffler) of these are Restricted with Carbon Deposits, then the Engine May Run at Idle but will Flood/Stall and Lose Power when you Try to Rev the Engine above Idle. The Following is a Basic Instruction File for Doing a Diagnostic on the Engine for this Problem. Any Input is Appreciated. **Remove the Muffler and Make Sure the Exhaust Port is Clear. If it is, then Try to Start the engine with the Muffler Off. If it Starts and Runs Properly, then Clean the Spark Arrestor Screen in the Muffler or Replace the Muffler if Required. Please, Do Not Hesitate, If you Hit a Snag or this Does Not Correct the Problem, I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Comments and Ratings are Greatly Appreciated. Thanks.

Respectfully

John