Stihl trimmer still giving me problems

Discussion in 'Mechanic and Repair' started by slimart01, Sep 9, 2010.

  1. slimart01

    slimart01 LawnSite Member
    Posts: 95

    I have an fs80 trimmer thats been giving me problems. Was idling rough so I replaced carb. That solved that problem. Then after running for a while the trimmer would just stop, not sputter, just suddenly die. Many users on here recommended replacing ignition coil. I replaced ignition coil as well as the spark plug. That solved the issue of it just crapping out suddenly. After about a month of no problems the trimmer now will run perfectly for about 5-10 minutes at 1/4 to half throttle then if you decrease throttle slightly it will try to die unless you quickly give it a lot of gas. Sometimes it will die and if you choke it crank it, half choke it with full throttle it will start back up but you have to maintain over half throttle to keep it from trying to die. Any ideas, its a good machine overall so I hate to junk it. Also, compression test was good.
     
  2. The Lawn Ranger CT.

    The Lawn Ranger CT. LawnSite Member
    Posts: 194

    Any number of things could be the issue...On the suddenly stop , I would check the wires leading to the on off switch , they wore through mine and would short the switch out every now and then, on the running with choke and half throttle, I'm leaning toward you still have some dirt in the carb, I would take it apart and soak it in some seafoam over nite then blow all the ports and jets out , some of the jet opennings are very tiny and the smallest bit of dirt and that's all it takes to make it not run right, also take the muffler off and check the carbon build up in the exhust openning on the motor, and also the muffler itself can be clogged, try running it without the muffler and see how it runs,....if ok then your muffler is clogged check the spark arrest screen, if clogged clean it with a wire brush or soak it with seafoam too and that should take the carbon build-up off, if push comes to shove you can run it without, it's just gonna be alittle louder thats all.
     
  3. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    Is the fs80 a four stroker? If it is you may want to adjust the valves.

    If it's a two stroke, have you changed out the intank fuel filter and checked the spark arrestor for carbon buildup?

    Sounds fuel related to me.
     
  4. Maico490

    Maico490 LawnSite Member
    Posts: 5

    Agree with Lawn Ranger that it could be carb related or as dutch says fuel lines or filter.
    Don't however blow any of the jets through with compressed air as there are check valves behind them and they are easily damaged. Use a piece of hose and blow through with your mouth. You should not be able to suck back if the check valves are OK. Nothing much should get past the screen under the metering valve so look there first.
     
  5. slimart01

    slimart01 LawnSite Member
    Posts: 95

    thanks guys, i was using it again today and it was giving me the same problems, at my last job i swapped fuel caps with a similar machine and it ran for 15 mins with no problems. so i'm thinking maybe the vent on the cap is clogged and causing a vacuum making it hard for the carb to pull fuel. Does this make sense? I'm gonna run it a little more and see if the problem goes away.
     
  6. hammmerhead

    hammmerhead LawnSite Senior Member
    from ozarks
    Posts: 266

    I run all Stihl hand helds as well. My arrestor screens clogged really fast on my small blowers, but not on my trimmers, edgers or backpack blowers. Removed the screens and all is well now.
     
  7. Alan0354

    Alan0354 LawnSite Platinum Member
    Posts: 4,458

    The last problem sound so much like my Honda trimmer after the first carb fail and they change to a new one. It started find, ran for 5 minutes and idle start slowing and choked. Once it die, it is hard to start and have to wot and pull until it started. It never had problem at WOT, just can't idle when hot.

    Dealer cannot find the problem after a few tries. I finally took out my old carb, opened it up, clear the block in the jet and put it onto the trimmer and never looked back!!!

    A new carb is not necessary a good carb!!! I opened it and can't find anything wrong. So it is in my draw now!!!!
     
  8. Chevy z71

    Chevy z71 LawnSite Fanatic
    Posts: 11,891

    stihl weedeaters are junk.
     

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