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Discussion Starter #1
My Stihl FS55 idles fine but will stall at 3/4-full throttle. I have emptied the fuel tank, cleaned the fuel filter, cleaned the fuel line (all looked clean but cleaned them anyway). I've removed the spark plug, re-gapped & cleaned it. Also pulled the exhaust & cleaned that. Cleaned the air filter also and tested without a filter. Nothing changed.

Any ideas. The fuel tank was perfectly clean as was the filter so I'd assume the carb is clean. Thanks!
Jim
 

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You have an issue with the either the high speed circuit or the accelerator pump. with today's fuels, issues pop up with swelling or shrinking orings. Most of these on the check valves are not repairable and the only way to take care of it is to replace the carburetor. What I suggest is remove the carburetor,open it up carefully and give it a good cleaning with brake clean and compressed air. And reinstall if that does not correct your issue you may need to put a new carb on this unit . I wish I could tell you how many carbs I have replaced in the last 2 years due to the fuel issues.new carb part #4140 120 0612
 

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Discussion Starter #4
Thanks a lot for the help. I figured it might be a carb issue but ruled it out when the fuel tank & filter were so clean. I will try cleaning it but would guess that its probably swelling or shrinking orings as you said. Thanks again.


You have an issue with the either the high speed circuit or the accelerator pump. with today's fuels, issues pop up with swelling or shrinking orings. Most of these on the check valves are not repairable and the only way to take care of it is to replace the carburetor. What I suggest is remove the carburetor,open it up carefully and give it a good cleaning with brake clean and compressed air. And reinstall if that does not correct your issue you may need to put a new carb on this unit . I wish I could tell you how many carbs I have replaced in the last 2 years due to the fuel issues.new carb part #4140 120 0612
 

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be careful with the compressed air. there are check valves in some carbs that you will blow right out of the carb if you use too much air.
 

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Discussion Starter #6
That is true. I have a 150psi compressor & its very hard to control the amount of air without releasing the pressure first.

Cleaned out the carb on the Stihl last night & it ran like new afterwards. Much easier than a motorcycle or lawnmower carb. Thanks guys!

be careful with the compressed air. there are check valves in some carbs that you will blow right out of the carb if you use too much air.
 
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