Sthil FS 55 RC brush cutter runs but has no power ?????????????

[patanga]

This brushcutter starts and runs but wont idle and has no power. The only way I can keep it running is either by continually triggering the throttle, or slowly open the throttle to about 1/3 and hold it in place. From there it will run (sort of) but produces no power and will not rev out. The power is insufficient to even engage the clutch.
The motor does have compression and spark.
There was some water and contamination in the fuel tank and so all fuel was replaced with new.
Carb, filters (Fuel & Air) hoses and spark plug have all been replaced with new parts.
Even with those parts renewed the running symptoms remain unchanged.

Ideas from the Sthil brains trust would be appreciated.
Thanks in advance.

 

[logert gogert]

New carbs don't usually come ready to run out of the box.
You will have to adjust the carb to were it seems it's running at its best.

 

[logert gogert]

And also, your model make and serial numbers would be greatly appreciated.
As for it will help us diagnose your problem better.

 

[bertsmobile1]

Welcome.
First question
1) genuine Stihl parts from a Stihl shop
2) parts from a real mower store or a real on line retailer
3) parts from a dubious supplier as found on Amazon & Ebay .
4) do ou run the recommened fuel : oil ration ar are you inclined to add a little extra oil ?

next, when was the last time you used it ?
Where was it stored between then & now ?
Was it running 100% the last time it was used ?

And a quickie to rule out mud daubers, remove the muffler and see how it runs.
This will be both very noisy and will most likely destroy the exhaust gasket.

 

[StarTech]

Can be the spark arrester on the muffler. It appears to be the screw in type. These are bad to clog with carbon. Also considering the age of these units it is possible that you need a carburetor repair. Considering the recent ridiculous changes at Zama it is just about as cheap to replace the carburetor as it is to get a full carburetor repair kit.

And also, your model make and serial numbers would be greatly appreciated.
As for it will help us diagnose your problem better.

In this case he posted the model number in the header. For Stihl it is about all that is need to look up the parts on the IPLs I have here. Now Stihl is constantly superseding PNs so only a Stihl can give the current PNs numbers for 4140 power plant.

 

[patanga]

Thanks for the feedback.
The make is a Sthil and model is FS 55 RC as listed in the subject line.

It has a new after market carb but runs exactly the same as it did with the O.E. Sthil carb.

I'm checking it over for a friend. The fuel supplied by the owner is fresh (today) premix.

My guess is that it had been sitting for a while but not more than a winter season. Stored in a garden shed.

I'm curious about the 'spark arrester on the muffler' comment by StarTech????? If they are clogged might that be a possible cause for the poor running a start condition??... If that is so is there a solution for cleaning the part?

 

[StarTech]

Yes as the engine can't breathe properly.

Remove the spark arrester and use a propane torch and burn off the carbon , just don't heat it as it can melt if too hot. If is one I thinking it has it take a 15mm deep well socket. Plus if it is the screw in type orchard wasps can plug them up but it is more likely it is just carbon plugged.

Make sure the carburetor is tuned correctly.
Max. permissible speed (with cutting attachment): 10,000 rpm (If above this tune rich to limit rpms)
Idle speed: 2,800 rpm

 

[Hammermechanicman]

Pull the muffler off and look at the piston for scoring. What you describe sounds like low compression.

 

[Fish]

A 16 mm or 5/8" socket to remove the little tube/screen on the muffler, it is plugged. Burn off the carbon or clean out the tube, and wash the filter in hot soapy water.

 

[patanga]

Thank you all. After removing the muffler I found no piston scoring so all good there. The spark arrestor was filthy and the muffler was carboned up as well. Muffler has been burnt out and after a light wire buffing the bulk of the grime on the arrestor was removed. I then dipped it in some petrol and let the rest burn off. All is now clean and again once back together I expect it will be able to breath and run once again. Been a long time since I've messed around with old 2 smokes but it's coming back to me. Appreciate the feedback.