Help! Trimmer bogging down!

Discussion in 'Lawn Mowing' started by battags, Sep 20, 2004.

  1. battags

    battags LawnSite Senior Member
    Messages: 607

    I have a three year old Stihl FS45 curved shaft trimmer that I use for edging beds (works great inverting it with the curved shaft). Lately its been bogging down and struggling for power. Under no load (line really short or not trimming grass) it gets up to high rpm's and sounds ok. The second you give it some line it boggs down again.

    I changed the fuel pick-up/filter, plug, and air filter, without any luck. I know that it's only a $150 machine, but don't want to dump it yet. Any ideas?

  2. pjslawncare/landscap

    pjslawncare/landscap LawnSite Bronze Member
    Messages: 1,410

    Check the screen (spark arrester) in the mufler. Remove it if its clogged. Opps I didnt tell u that :cool2:
  3. bushtrimmer

    bushtrimmer LawnSite Senior Member
    Messages: 351

    clean out the spark restrictor screen in the muffler.
    Not sure about that machine but you can probably pull it out w/ needlenose pliers. It would be irresponsible of me not to tell you it needs to be replaced.
  4. imograss

    imograss LawnSite Senior Member
    Messages: 796

    Clean the carbon from around the piston carefully. I leave my spark arrestors off and use Opti 2. It has cut my carbon buildup WAY down.
  5. aspenlawn2000

    aspenlawn2000 LawnSite Member
    Messages: 9

    I seem to have a bogging problem, and I have to move the choke lever just a little and it runs just fine. Try that before anything else
  6. mbricker

    mbricker LawnSite Senior Member
    Messages: 505

    Try the easy stuff first, spark arrestor screen, choke position etc. If no change, try this--it's not difficult. (This may be what imograss is referring to)

    Remove the muffler, and of course any housing that is over the muffler. Look into the exhaust port and you may see it is partially blocked by a carbon buildup. With the piston blocking the port, use a small screwdriver to scrape and break loose the carbon. You may see that the port is restricted by half its area or more. You are doing this with the piston blocking off the port so chunks will not end up in the cylinder.

    Be careful not to jam the screwdriver in too hard and damage a ring or the piston itself. Turn the motor up and shake (or blow if you have compressed air) the carbon out of the port. With the plug wire off the plug, pull the starter rope to spin the motor and blow any remaining loose chunks out. When you are satisfied you have got the port scraped clean, reassemble. It should run much better.

    While you have the muffler off, look through the various passages and make sure there is no clogging, and make sure the spark arrestor screen is not clogged up. But I have never had either muffler or screen clog up, it's always the exhaust port in the cylinder.

    I did this Sunday nite to an Echo trimmer, and it made a world of difference, like I knew it would--I had been putting it off, and struggling with a weak trimmer. Ah the joys and pain of procrastination.

    BTW, while you were fiddling with it, you didn't change the carb settings, didja? Might have to re-adjust them, if you have changed 'em. And one other thing--I think this condition is mostly caused by starting the trimmer, moving it to partial choke while it gets warmed up, and forgetting to move it to choke off--fully open choke--and continuing to use it. Yeah, that's what I do too.
  7. Lbilawncare

    Lbilawncare LawnSite Bronze Member
    Messages: 1,119

    After doing what the guys above recommended (which was good advise) run a capful of Sea-Foam through it. You can also try using Brakekleen to clean the carb area and where the ignition module makes contact.
  8. battags

    battags LawnSite Senior Member
    Messages: 607

    No spark restricter screen on this model. I already thought of that and it was the first thing I took off of my fs85 when I got it. The fs45 has a short exhaust port and doesn't appear to be clogged. I'm going to pull the muffler in the morning.

    I have never had one bogg down like this. I'm almost ready to drop it off at the dealer.

  9. matthew horner

    matthew horner LawnSite Senior Member
    Messages: 696

    I have a new stihl (I think fs85). Would taking the arrestor off of it make it stronger????
  10. GreenMonster

    GreenMonster LawnSite Silver Member
    from NH
    Messages: 2,702

    This may be a little far fetched, but is it possible that you have a damaged fuel line -- possibly dry rot? Does is seem as if it is starving for fuel?

    I had a similar type problem with an Echo, and the fuel line inside the tank was damaged. I snipped off the bad part and the problem went away.

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