2 stroke Stihl guys (FS 85?)

Discussion in 'Lawn Mowing' started by Envy Lawn Service, Aug 3, 2006.

  1. Envy Lawn Service

    Envy Lawn Service LawnSite Fanatic
    Posts: 11,062

    OK guys... could yall help me make sense of this?

    Evidently I lost a bump head spring, which allowed my line to advance itself. It stayed close enough to just the right length through most of a spool that I didn't even realize it until I went to do a rough cut.

    I was cutting along side a long driveway going up to one of my mountain-top residential sites. The line pulled out too long and I didn't have my clippers with me as I had a spare spool in my back pocket. So well I burned off the excess on the pavement. Right at the end of the driveway cutting it did it again. So I attempted burning it off again, which for reasons that puzzled me at the time, I couldn't seem to get it to happen. (Didn't realize the spring was not in the head)

    So I'm reving and burning, and it shuts off. I thought I was out of gas, so I went to fill up. I had pretty much burned a full tank. Filled it up. Couldn't get it to crank back.

    Turns out later that I guess I burned up the ignition coil. The trimmer is an '02 I think, certainly on the orginal coil, it was near 100 degrees out and I had been running HARD.

    Well, I bought and installed a new coil ($30). It fired right up. But the top end was trashy. I couldn't find my feeler gages, so I reset the air gap on the coil with a business card. (I figured that was about right).

    Well, the top end was still trashy, so I attempted to adjust the high speed screw. It got worse, until I started backing it down below the normal +3/4 turn. I backed it down to -0- position and it runs great.

    But what sense does that make???????

    I'm afraid to leave it there where it's running good.
    What would you do?
     
  2. dvmcmrhp52

    dvmcmrhp52 LawnSite Platinum Member
    from Pa.
    Posts: 4,205

    Your engine will most likely overheat from running too lean if you leave the carb adjusted that way.
    Set the coil to the right spec and go from there.
     
  3. lawnboy dan

    lawnboy dan LawnSite Gold Member
    Posts: 3,712

    sthil ing coils are junk. i have been tru a lot of them. no more sthil for me.
     
  4. Envy Lawn Service

    Envy Lawn Service LawnSite Fanatic
    Posts: 11,062

    Well, I went back out before reading this and ran a bit more than a tank through it, mostly set that way, and luckily I didn't burn it down.

    At best, it's idling pretty good but running pretty darn trashy. It hesitates and misses and so forth. When I turn the high screw down I get my screaming revs back though. Turn the screw back towards where it should be set and it starts going flat.

    I don't know what the spec is on the coil air gap. It's not in the manual. So I set it with a business card, figuring the air gap spec was likely pretty tight/close.

    As for the Stihl coils, I really can't complain, as this one is the first one I've had to replace, and this trimmer is at least 4 years old. But with this new coil, it's not running as well as it did before the original went out.

    To those of you who have replaced coils on your Stihls, what is the deal with the spacers that go on behind it to sit it out farther than the original?
     
  5. dvmcmrhp52

    dvmcmrhp52 LawnSite Platinum Member
    from Pa.
    Posts: 4,205



    Most coils go due to overheating.
    Operator error.
    Trimmers don't need to be running full throttle to be effective, they work quite well at less than half throttle for the vast majority of use.
     
  6. walker/redmax

    walker/redmax LawnSite Senior Member
    Posts: 367

    OK, the secret to dealing with problems like this is simple. Just follow my step by step instructions.
    1. load your trimmer up and drive to the dump.
    2. dump your trimmer.
    3. drive to the Redmax dealer.
    4. you guess from hear (hint: BCZ3000S)
    :laugh: j/k if you are happy with your Stihl, I would recommend that you have your dealer look at it.
     
  7. dvmcmrhp52

    dvmcmrhp52 LawnSite Platinum Member
    from Pa.
    Posts: 4,205



    We've never replaced a coil.............
    The spacers may not be neccesary for your particular trimmer, they may have been for "optional" spacing if needed.
     
  8. Envy Lawn Service

    Envy Lawn Service LawnSite Fanatic
    Posts: 11,062

    Well, the engine is used in several Stihl applications. So the coil had instructions with it. But there were no words. Weird. It had a little thing showing to flip the page for the other applications.

    On the side I was looking at it had a diagram, then an eyeball with a line to the numbers on the bad coil. Those matched. Then it showed removing the old coil and installing the new one with the spacers.

    I could always remove it, take off the spacers, re-install, re-gap and try to see it there is any difference. Somehow I doubt it. I figure the spacers were to put the coil a little farther off the engine.
     
  9. DFW Area Landscaper

    DFW Area Landscaper LawnSite Silver Member
    from DFW, TX
    Posts: 2,116

    Stihl coils are guaranteed for 5 years. I am not sure what an FS-85 is, but I would guess it's the same engine as the FS-80 & FC-75.

    I spoke with Stihl a few weeks ago and they said they almost never see the coils on those engines fail.

    You can call 1-800-GO-STIHL and they are EXTREMELY helpful on that line.

    One thing that is often overlooked is the vent in the fuel cap.

    Later,
    DFW Area Landscaper
     
  10. milo

    milo LawnSite Bronze Member
    Posts: 1,259

    sounds to me like you burnt the piston. if its a 02 i would just buy a new trimmer a stihl fs90 4 mix. way less vibration and nice.
    and red max is a joke. i just bought one of there hedge trimmers they are weak. stihl and echo kill them easy. back to your problem:::
    1. you burnt the piston from overheating and that would cause it to run like that on the top end. i know from all my dirt bikes i have and had...
    2. messed up the muffler from overheating.
    3. put in a new plug and make gap a little smaller and also make sure your gap on the coil is set right.
    if new plug and right gaps dont fix it just buy a new trimmer. you are just gonna keep wasting money on the old one that will not ever run right. i always replace my hand held items every year and at most every 2.
    envy also did you try echo string yet????
     

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