stihl fs80 string trimmer lacks power

Discussion in 'Homeowner Assistance Forum' started by rknarr2, Aug 12, 2009.

  1. rknarr2

    rknarr2 LawnSite Member
    Messages: 16

    i have a stihl fs80 string trimmer that I bought used off ebay recently. The EPA sticker on the shaft has 1998 written in it so that is why I believe it was made around 1998 period. The carbeurator is a stihl S28D that has an adjustable screw for air intake into the carbeutor and thought that it might be the problem with it but then again I thought maybe its the low idle screw that needs adjusted I simply do not know and just guessing.
    Here is what I have done to try to fix it as follows:
    I tried to take the spark plug wire off the spark plug but it was stuck on to the spark plug but when I pulled on it the other end of the spark plug boot ripped the wire out of it. I took the stihl fs80 over to my brother in law and he put the wire back through the boot and I guess clipped it into that wire spring inside the boot. Well, he put the spark plug and attached it to the spark plug wire and put it up against metal on the side of the weedeater and pulled the starter pulley to make sure that it was creating a spark. That way he knew the coil was working and that the spark plug was working, too.
    I put on a carbeurator kit, cleaned the orfices with starter fluid, cleaned the fuel tank, put on new fuel line with fuel filter and return lines. That did not seem to fix the problem I am having with it. When I start it up and let up on the trigger it wants to die off on me and also if I try to use it with the trigger fully pressed it gets sluggish when I cut weeds with it. Thank you for your assistance.
    Regards, Robert
    Last edited: Aug 12, 2009
  2. lawnmon

    lawnmon LawnSite Member
    Messages: 116

    First, check for leaks around the carb. There is a black plastic spacer flange, part # 4137-121-1601 or 4137-121-1600, that holds the carb away from the cylinder. Check it for cracks. If the trimmer gets worse as it heats up, this could be the problem.

    But, I'll bet you put a new carb on it, it'll run like new.

    Good luck
  3. rknarr2

    rknarr2 LawnSite Member
    Messages: 16

    That might work putting on a new carb but I wanted to exhaust other less expensive means to avoid it. I will check that black plastic spacer flange for cracks and check for leaks around the carb, too. Thank you for the suggestions.
  4. rknarr2

    rknarr2 LawnSite Member
    Messages: 16

    I received the following suggestions from an ebay seller who is selling small engine manuals as follows:
    check your plug and valve? as long as its clean and properly gapped. single fire doesn't always mean repetitious fire. what about the valve...make sure its not sticking any. did you take and make sure float was internally dry? and needle valve and seat were clean and properly placed?
  5. milike

    milike LawnSite Member
    from MI
    Messages: 169

    a few $ for a new zima carb and you'd be all set
  6. lawnmon

    lawnmon LawnSite Member
    Messages: 116

    One other item to check is the exhaust/muffler for restrictions. Many are very clogged and they won' run well like that.
  7. rknarr2

    rknarr2 LawnSite Member
    Messages: 16

    I put a brand new muffler on the weedeater so the screen is not clogged up. I was told to remove that screen on the old muffler on the phone from a stihl service person but it was all ready taken out. Thank you.
  8. rknarr2

    rknarr2 LawnSite Member
    Messages: 16

    I took the spacer flange part, 4137-121-1600, off and cleaned it up with soap and water. I then checked it for cracks and I found a stress crack along the entire side wall which was probably from a person who over tightened the bolt(s) that caused the stress crack to occur or when I took the bolt(s) out I caused the stress crack by pushing down on the bolt as I loosened it. In any case, I will have to replace it. Thank you lawnmom I will let you know after I get a new one if it fixes the lack of power problem. Regards, Robert
  9. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    I had a similar problem and I got so tired of it doing that, I accidentally figured something out.

    Now I can't recommend you do it, but just like yourself I replaced the carburetor and hence had a spare...
    That wasn't the only thing I had replaced but long story short I was a bit pissed, so one day I took a
    needle nose vise grip and clamped it on to the HIGH adjustment screw, the plastic part.

    Then I turned it up to where the plastic hits that stop and kept going until that POS
    plastic sleeve broke and allowed the adjustment screw to go past the stop.

    Once that was done it was easy to adjust it, and I got it running pretty good
    with the high end screw somewhere past the manufactured stopping point.
    Doesn't run 100% perfect but it's close enough for me.

    As I said I can't tell you to do that, but when I asked about this at the dealership they said the procedure isn't unheard of.
    I also heard other folks saying you just have to learn how to 'adjust' it...

    Mine's an FS-80r, 2001 model.
    Good luck.
  10. rknarr2

    rknarr2 LawnSite Member
    Messages: 16

    I put on a new flange spacer but that did not help.
    As I mentioned above, I have also put on a new muffler and put on a carburetor kit but those did not help either.
    So, maybe if I take the valve seal out of the carburetor and clean that in mineral spirits and replace the spark plug might be the next things I will try.
    If that would not fix it, then should I look at taking off the cylinder and looking at the valves to see if they are sticking or taking a look at the idle speed on the carburetor. I am not sure what to try next running out of options and ideas. If you want to know what my problem is please review the initial thread above. Thank you.
    Last edited: Aug 27, 2009

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