# stihl fs 110 runs but not good



## lanche (Jun 8, 2005)

I had my neighbor bring me his stihl 110 weed eater to tune up. I fired it up but at full throttle it barely runs. I changed the fuel just to make sure but still the same. If I press the primer bulb while it's running it it seems to run pretty good for a second but then starts to run bad again... any ideas...thanks


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## 30yearTech (Sep 14, 2006)

check for a plugged exhaust / dirty spark arrestor screen


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## lanche (Jun 8, 2005)

Ok I pulled the screen out and it looked very clear


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## lanche (Jun 8, 2005)

Does anybody else have any other ideas...thank you


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## Sir Thomas (Dec 7, 2013)

What brand of Carburetor does it have. When you prime it you actually purge it bringing in fresh fuel so that tells me you have carb problems or a leak somewhere. What's the condition of the fuel filter. When you prime it do you see air bubbles in the intake line (the one with the filter)? How long does it take while priming for the return line to show fuel going back to the tank with no bubbles?
Have you tried a carb rebuild kit?


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## 30yearTech (Sep 14, 2006)

Very possibly there is a leaking check valve in the carburetor body, these are not serviceable parts. A new carburetor should take care of your issue.


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## lanche (Jun 8, 2005)

Is there any way to check for a leaking check valve before I try to rebuild the carb?


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## Sir Thomas (Dec 7, 2013)

Take the carburetor apart. There is probably two check valves. One for the idle and the other for the run. Both should be in the metering chamber. This is indicated by a H screw and a L screw.
I would know better how to describe if I knew the Brand, Type and Model but the ones I've worked on the idle has a brass ring. Make sure the L screw is at least 2 turns out. Take a fuel line tube and place it snuggly on top of the hole and blow gently. You should be able to blow through the tube. If you can back the L screw one more turn. After you feel you can blow through the suck gently. You should hear a click and not be able to suck. If you can suck air then that check valve to bad.
Do the same to the other check valve. The ones I've worked on the check valve is in the nozzle. There is a little hole towards the side. Repeat the steps above.


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## 30yearTech (Sep 14, 2006)

lanche said:


> Is there any way to check for a leaking check valve before I try to rebuild the carb?


If the problem is a leaking check valve, then a rebuild kit is not going to fix it. If the problem is due to stiff diaphragms or with the inlet metering needle or fulcrum arm then a kit could be the ticket.

Looking at the IPL for an FS 110 they show to have used at least 5 different C1Q Zama carburetors on them.


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