Small Engines (Lawn Mowers, etc.): lawn mower and chain saw wont fire, head valve engine, adjustment screws

Question
this not a question i was not sure how to relate back to you on the chain won't fire and still won't lawn tractor last fall acted like it had a bent shaft still does, i think you are very good on advise..somethings just ware out especially when they are cheap,but i have learn from your feed back and i am sure i will have future questions because i still buy lowes stuff thanks john and all for the help! steve

Answer
Hello Steven:

1- On the Mower Engine that Seems like a Bend Crankshaft; Is it and OHV (Over Head Valve) Engine? If Yes, then the Valve Clearance May Require Resetting. When the Valve Clearance Gets Out of Adjustment on the OHV Engines, they Act like the Crankshaft is Bent. They Turn 3/4 Turn and then Stop or Drag for 1/4 Turn. For Both Units; Send me the Model and Type or Spec Numbers Off the Engines, Please. With these I can Locate the Proper Manuals and Better Assist you. On the Engine, the Model Numbers May be Stamped Into the Blower Housing (metal engine cover) Above the Spark Plug. 2- For the Chainsaw; here is a Diagnostic File I Made Up for Chainsaws. **Here are some Diagnostic Instructions to Do on the Trimmer/Chainsaw to Locate the Hard/Not Starting Problem. 1- Check the Spark. If Not Firing, then Replace. 2-  If the Plug is Firing, then First, Remove the Muffler and Check for Blockage in the Exhaust Port and the Muffler. Check the Spark Arrestor Screen in the Muffler, too. 3- If these are Clear, then Pour a Small Amount of Fuel Mix Into the Carburetor Throat with the Throttle at Full. With the Throttle Still at Full, Try to Start the Engine. If the Engine Starts and Quits, Check the Fuel Filter and Lines. If these are Good, then Remove, Disassemble and Soak the Carburetor Overnight in Carburetor Cleaner (I Use Gunk). I have Found that Most People can Use a Breakdown/IPL and Disassemble the Carburetor Enough for Proper Cleaning. You Only have to Remove the Bowl, Float Pin, Float and Needle Valve and Any Adjustment Screws that Go Into the Carburetor Body. The Welch Plugs Do Not have to be Removed. Then Soak the Carburetor Body and Parts in a 1 Gallon Can of Gunk Carburetor Cleaner Overnight. The Can has a Parts Tray Inside it for the Small Parts. Once the Carburetor and Parts are in the Cleaner, you can Replace the Lid for Safety and to Prevent Accidental Spillage. Then Blow Out the Passages with Compressed Air. Install New Parts if Required. Set the Air Mixture Screws as Follows; All the Carburetor Adjustments are the Same for Lawn Mower and Trimmers. There are Several Location for the Air Mixture Screws. The Idle Air Mixture Screws are Usually Located at the Top of the Carburetor Bowl and the Top of the Carburetor Body. If the Main Air and Idle Air Mixture Screws are Side by Side on the Side of the Carburetor, then the Idle Air is the Farthest from the Engine. The Main Jet Air Mixture Screw is Located in the Bottom of the Carburetor Bowl or Beside the Idle Air Screw on the Side of the Carburetor Body. Some of the Older Model Carburetors have the Main Jet Mixture Screw Straight in from the Top of the Carburetor Body (this is Rare anymore). If you have Cleaned the Carburetor (Disassembled and Soaked Overnight in Carburetor Cleaner (I Use Gunk). Then Blow Out the Passages with Compressed Air and Install a New Kit if Required. Now Setting the Air Mixture Screws:  ****Turn the Idle Air and Main Air Mixture Screws In Until SNUG **Don Not Jam** Then Reverse Both Screws 1 1/2 Turns. Holding the Throttle Full Open, Start the Engine. Turn the Main Air Mixture Screw Clockwise Until Proper Revs are Obtained. 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 Mixture Screw so there is No Hesitation when Throttling from Idle to Full Throttle. Reset the Engine Idle if Required.**** 4- If No Fire at the Plug, then Remove the Coil Shut Off Wire from the Kill Switch. Check for Fire. If No Fire, then Remove the Blower Housing and Remove the Ground Wire from the Coil. Check for Fire. If Still No Fire, then the Coil/Ign Module is Bad. 5- If there was No Response from the Engine When the Fuel Mix was Poured Into the Carburetor Throat, then Check the Compression. 6- If the Engine has Compression, Fuel and Spark, but Still Does Not Run, then Check the Flywheel Key. It May be Damaged or Sheared and has the Plug Firing at the Wrong Time During the Power Stroke (compression).** 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. Thanks.

Respectfully

John