QuestionQUESTION: Hi John,
Background: I have a two and a half year old Stihl FS55R string trimmer that, because it wouldn't run for more than 10 seconds, I rebuilt the carburetor, replaced the fuel lines from the gas tank to the carburetor and the fuel filter. Now it runs, but I need to keep me finger on the throttle or it will stall. So I have to run it at full throttle or it will stall. I tried tweeking the carburetor but that didn't help. I looked into replacing the Zama carburetor only to find out it has been discontinued (not too good for a 2 1/2 year old michine). I located the replacement carburator from the local Stihl dealer that I purchased the trimmer from. They want $56 (or 25% of the cost for a new trimmer). an't see myself doing that.
Now the long awaited question: Do you have any next step suggestions to get the trimmer running properly before I go out a purchase a new trimmer (It will not be a Stihl)?
Thank you for your time and assistance,
Frank
ANSWER: Hello Frank:
>>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.
>>If the Exhaust Port or Muffler are Restricted you will have this Problem.
>>If the Carburetor Metering Needle Valve is Not Set Correctly you will have this Problem.
>>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 5 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
---------- FOLLOW-UP ----------
QUESTION: Hi John,
When I rebuilt the carburetor I also checked the exhaust port for blockage and wire brushed the spark arrestor screen. So I don't believe the exhaust is causing the problem. As for the inlet needle valve, that was replaced when I rebuilt the carburetor. I adjusted the metering lever as explained in the directions. If that is the problem, do you think I set it too high or too low?
Regards,
Frank
ANSWER: Hello Again Frank:
>>Remove the Spark Plug and Check for Fouling. If the Plug Looks Clean and Not Fouled, then
>>You have the Needle Valve set too Lean. If it Looks Fouled, then you have it set too Rich.
>>Can you Set the Idle Screw to make the Unit High Idle?
>>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 ( Usually the H 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. **Carefully Use your Finger and Move the Governor Arm to Rev the Engine (on Chainsaws and Trimmers Use the Trigger to Rev the Engine) Until you Reach Max RPMs (on Chainsaws and Trimmers, the RPMs are Not Set to MAX. Set to Max and then Reverse the Setting Screw 1/4 or 1/2 Turn. If the H Mixture Screw is Set too High; the Engine will be Starved for the Oil in the Gas and Damage the Piston and Jug/Cylinder) and the Engine is Running Proper at Full Throttle Up a Grade and for Chainsaws and Trimmers they Do Not Bog Down Under a Load. 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 Rapidly Throttling from Idle to Full Throttle. Reset the Engine Idle if Required.****
>>As Always, 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 5 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
Hello Again Frank:
>>Thanks for the Ratings.
>>I See from your Post you are Still having Problems with Idle.
>>The Next Component to Check is the Carburetor Mounting Gasket and Mounting Surfaces.
>>Make Sure the Gasket is Installed so the Small Vacuum Port is Opened to the Carburetor and that the Mounting Surfaces are Not Warped.
>>If these are Good, then Check the Jug/Cylinder Bolts and make Sure they are Torqued Correctly.
>>You may have to Remove the Jug and Clean and Replace the Jug Sealant. This is Usually a Bead of "Ultra Black" Silicone.
>>Also Check the Flywheel Key and Ensure it is Not Damaged. Sometimes when the Key is Slightly Damaged it will Cause this type of Problem. Is is Rare, but I have had this be the Cause for this Problem at least Once in the Shop.
>>Till Next Time. May All Your Mechanical Problems be SMALL ONES and as Always, May the All Mighty Bless You and Yours. Be Safe and Happy.
Best Wishes and Good Luck
Respectfully
jbridger (John)
---------- FOLLOW-UP ----------
QUESTION: Hi John,
Now you got my attention again with you last response. I can certainly check the mounting gasket, but what are the Jug/Cylinder bolts? The the Jug the spacer between the carburetor and the intake port? If it is, currently there is a gasket (original, but in very good shape) on both sides. Should I replace the gaskets?
Also if the flywheel key is what I think it is (the small piece of metal that prevents the flywheel from rotating on the drive shaft) wouldn't that through the timing off?
Thanks again,
Frank
AnswerHello Again Frank:
>>lol. No Worries.
>>The Jug Bolts are the 4 Bolts that Attach the Engine End Plate to the Engine Body. It is Usually Square with a Round Recess that Sets it Centered in the Engine Body. If these Loosen or the Seal Leaks the Engine cannot Idle Correctly, but will Run at High RPM's and Sometimes if the Leak is Bad enough it will Not Start.
>>The Carburetor Gaskets may still be Good, but if they are Not Aligned Correctly or are Leaking, then you have the Idle Problem.
>>If the Flywheel has a Mark of Any Kind on it, then Replace it. The Key will Throw the Timing Off, but a Slight Indent in the Key can cause the Timing to be Off enough to cause Idling Problems.
>>As Always, 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 5 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
Hi Frank:
>>Again, Thanks for the Comments and Ratings.
>>I Just Read you Comments and wanted to Ask if you are Sure you have the Adjusting Screws in the Correct Holes.
>>One of the Mechanics had this as an After thought and wanted me to Remind you and Others that the Mixture Adjusting Screws are Different and Must be Installed in the Correct Hole in Order to Adjust the Air/Gas Ration Correctly.
>>Till Next Time. May All Your Mechanical Problems be SMALL ONES and as Always, May the All Mighty Bless You and Yours. Be Safe and Happy.
Best Wishes and Good Luck
Respectfully
jbridger (John)
