QuestionHi i have been looking about on net for help.I cannot get the trimmer to start if i pull it a few times i get a backfire if the choke is full on.I have a spark at the plug would i be right in thinking it is the ignition coil?
thanks Shaun
AnswerHello Shaun:
>>This Problem is Usually caused by either the Exhaust Port and Muffler being Restricted by Carbon, the Flywheel Key being Damaged and Sometimes from the Carburetor being Dirty (internal passages restricted with Varnish).
>>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. Some Mufflers will Split apart for Cleaning of the Screen and Some are Screwed/Bolted to the Outside and on Others the Muffler has to be Replaced.
>>The Following is a Basic Instruction File I made for Removing the Flywheel and Replacing the Flywheel/Flywheel Key.
>>Remove the Cover that Houses the Starter Assembly.
>>Remove the Spark Plug and Use a Bolt the Same Diameter and Threads as the Spark Plug and About 3" Long.
>>Thread the Bolt into the Spark Plug Hole Until it Engages the Piston.
>>Slowly Tighten the Bolt Until you have Locked the Piston and it Does Not Move. **BE CAREFUL A LOT OF TORQUE IS NOT REQUIRED. PISTON DAMAGE CAN OCCUR IF TO MUCH TORQUE IS USED ON THE STOP BOLT**
>>Now Remove the Flywheel Nut.
>>Use a 3 Jaw Puller and Attach the Puller to the Flywheel.
>>Look for a Puller with Flat Jaws. These Slide Under the Flywheel and Allow for Easier Removal.
>>Tighten the Puller and then Hit the Puller with a Hammer. Tighten and Hit Again Until the Flywheel is Loose and Can be Removed from the Crankshaft.
**Note the Key that Aligns the Flywheel to the Crankshaft.**
>>This Key is Most Likely Sheared or Bent and Causing the Plug to Fire Slightly Out of Time and Causing a Compression Lock. There is Not Enough Compression to Kick Back But Enough to Cause the Engine to Seem to Have High Compression or it May Seem to have Low Compression and Not Backfire at All.
>>**Some of the Newer Units have the Flywheel Key as a Part of the Flywheel and the Complete Flywheel has to be Replaced.**
>>The Following is a Basic File I Made for Cleaning Carburetors. An Illustrated Parts Breakdown will Assist you in the Disassembly and Assembly of the Carburetor. Any Input is Appreciated. Even though the Carburetor Looks Clean, the Internal Passages May be Restricted with Varnish that Gas Causes to Build Up over Time.
>>Spray Cleaners Remove this Varnish in Layers, so Soaking is the Only Sure Way to Remove ALL this Varnish.
>>I have Found that Most People can Use a Breakdown/IPL and Disassemble the Carburetor Enough for Proper Cleaning.
>>Remove Any Adjustment Screws that Go Into the Carburetor Body. The Welch Plugs Do Not have to be Removed.
>>If you are Able to Remove and Disassemble the Carburetor and Keep the Gaskets Intact, then Usually these Gaskets can be Reused. The Only Parts you May Need to Replace are the Needle Valve and Metering Pump Diaphram.
>>The Metering Pump Diaphram is Under the Carburetor Plate with 4 Small Screws in it.
>>The Dowl on the Diaphram should Just Touch the Metering Jet Actuator Arm.
>>The Actuator Arm is Adjusted by Carefully Bending the Actuator Arm Up or Down to get the Correct Clearance.
>>If you Order a Kit, then Replace All the Old Components with the New Ones in the Kit even if the Old Parts Look Good.
>>Once Disassembled, 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.
>>***(Do Not Use High Pressure Air for the Zama Carburetors, they have Check Valves for the Primer and these are Usually Blown Out of the Carburetor if Not Careful. Allow the Zama Carburetor to Set on a Drip Pan and Dry)***.
>>****All the Carburetor Adjustments are the Same for Lawn Mower and Trimmers.
>>If the Main Air and Idle Air Mixture Screws are Side by Side on the Side of the Carburetor, then the Idle Air is Nearest the Engine.
>>****Turn the Idle Air and Main Air Mixture Screws In Until SNUG **Do 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.****
>>If you have Questions, Please Ask. The links above Provide Good Directions on Cleaning the Carburetor. Make sure you use an Compressed Air to Blow through all the Carburetor Passages to make sure they are Clear.
>>1- http://www.repairfaq.org/samnew/lmfaq/lmclctc.htm
>>2- http://www.cpdonline.com/692509.pdf .
>>If you Hit a Snag or this Does Not Correct the Problem, I Hope to be Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Be Safe and Happy. Thanks.
Good Luck
Respectfully
John
PS: I am Allowed to Answer 3 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. All Follow up Questions are Accepted at Any Time. Comments and Ratings are Greatly Appreciated. Thanks.
Respectfully
John
