QuestionI have a Sears Craftsman "Weedwacker" string trimmer, model #358.798530. I got this from a friend because it would not start. I started with spark, replacing
the spark plug and re-gapping the magneto and plug. I definitely saw a pretty good spark, but it still had trouble starting.
I then took the carburetor partially apart, but everything looked clean and normal, so I put it back together (re-using old gaskets). By playing with the primer and the choke a lot, I could get it to fire for a couple of seconds, but then it would die.
Then I started playing with the mixture screw. I wound up turning it alot counter-clockwise (enriching the mixture?), and got it to run on half and then no choke for 15 or 20 seconds, but it would again sputter out (by the way, all this is on full throttle - it dies immediately if I close the throttle).
So, now I have taken it completely apart. There is carbon on the top of the piston and in the muffler, but the ring is not broken and there does not seem to be any scoring on the cylinder wall (although, it doesn't appear honed like most 4-cycle cylinders I have seen before). Other than trying to plug the spark plug hole with my thumb, I don't have any way to test if it has compression, and the thumb test isn't working well on such a small cylinder.
So, I am stuck, hoping for some advice. Any suggestions where to go next with this thing?
Thanks
AnswerHello Don:
The Cylinder Should be Smooth and Shiny. No Marks like in the 4 Cycle Engines. When New there are Marks in the Cylinder, but they Disappear in a Few Operations of the Trimmer. If the Muffler and Exhaust Port were Clogged with Carbon, that Could be the Reason Why the Engine Would Not Take Fuel. Reset the Carburetor and Try the Engine with a New Muffler and the Exhaust Port Clear of Carbon. You May have to Remove, Disassemble and Soak Overnight in Carburetor Cleaner (I Use Gunk). Then Blow Out the Passages with Compressed Air and Install a New Kit if Required if the Clean Exhaust Por and New Muffler Do Not Solve the Problem. From your Description, I'm thinking the Muffler and Exhaust Port. Here are the Instructions for Setting the Carburetor Mixture Screws. All the Carburetor Adjustments are the Same for Lawn Mower and Trimmers. There are Several Locations 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.**** If the Above Procedure Cannot be Performed and the Engine Will Not Operate Properly, then Remove, Disassemble and Soak Overnight in Carburetor Cleaner (I Use Gunk). Then Blow Out the Passages with Compressed Air and Install a New Kit if Required. Hope this Helps. I am here if you Require more Assistance. Let me know what Happens, Please. Thanks.
Good Luck
Respectfully
John
