STihl fs-85 pro problem

Discussion in 'Mechanic and Repair' started by K c m, Jun 29, 2006.

  1. K c m

    K c m LawnSite Bronze Member
    Messages: 1,313

    First off my trimmer is 5 and a half yrs old with no new parts (keep in mind) The trimmer was running great for the first part of the season but for the last 3 weeks it has been running fine for about 15-20 min and shutting down. Try to restart it and nothing. Next property it starts right up and runs fine agian for about 15 minutes.

    First off i thought it was a faulty connection with the sparkplug wire and the sparkplug. So i cut the old end and stripped it and put the coil back in and put it back in its housing. (still doing the same thing)

    So i took off the whole unit magnets and all (since its one unit) and figured maybe they needed to be cleaned off. ( same thing)

    Im kinda at witts end right now since i have a stupid home owners as a backup. IM hoping its not a big issue maybe just needs a replacement wire magnet and coil housing for the sparkplug. Im hoping thats just it tho :confused:

    any help would be great. I need any comments as soon as possible please. ALl this rain and now its hot and humid GRRRRRRRRRRRRRRr.

    thanks in advance
    rob KCM landscaping.
  2. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Messages: 1,164

    Make sure your tank is venting properly and your fuel lines are not dry and cracked. After checking these things, do you have an inline spark tester? When it shuts down test the unit for spark I have changed lots of ignition coils on Stihl handheld.
  3. sgtgm5

    sgtgm5 LawnSite Member
    Messages: 81

    Sounds like it is your ignition module. I just had the same proplem with my fs 85 and is almost as old. I got the part for 32.00.
    It is the module that your spark plug is hook onto. It heats up and breaks contact not alowing spark to transfer after a period of time and then cools down allowing spark.. Let me know how it goes.
  4. K c m

    K c m LawnSite Bronze Member
    Messages: 1,313

    thanks a lot guys. Ya im banking thats the problem. It produces electricity from the rotating magnets.

    but ya when i have some time ill snag one. That trimmer is a beast :weightlifter:
  5. sgtgm5

    sgtgm5 LawnSite Member
    Messages: 81

    I love the fs 85. I did have a problem before fixing it about why dont i just bye a new fs 100. I really needed a trimmer that could use the attachments cause i have a big hedge job coming up. The 100 also can use the attachments. Im glad now that i fixed the old one. Now i have that fixed and a echo 2601. LIke both but sthil is top of the food chain when it comes to weedwhackers. I will soon bye a fs 100 when i decide what type of trimmer rack to bye. Good luck for the rest of the season and hope you dont have to put no more money into it.
  6. K c m

    K c m LawnSite Bronze Member
    Messages: 1,313

    SG. let me ask you something. I took a look at the one i have and when i reinstalled it after cleaning it i wasn't sure how close to the magnets to get. How close did you install the thing? cause u can get a good 8th off the magnets it if u want or as close as a mm. ??? what did u do or does it matter?
  7. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,362

    Use a paper tab card to adjust...needs to be pretty close. Maybe the width is .007"....never worried just used the container that spark plugs comes in the set the gap on between the coil and magnets.
  8. lawnboy dan

    lawnboy dan LawnSite Gold Member
    Messages: 3,711

    coils have gone bad on every one of my sthil edgers and weedeaters. one went out on my extended hedge trimmers too. - i dont buy sthil products any more. the coils shoild have a lifetime waranttey but dont! sthil stuff has gone to crap!
  9. 6'7 330

    6'7 330 LawnSite Bronze Member
    Messages: 1,821

    Ignition coil is a good bet.There is a 5 year parts and labor warranty on that module.
  10. lawnboy dan

    lawnboy dan LawnSite Gold Member
    Messages: 3,711

    it should be lifetime like echo has! 5 yrs isnt long enough. the ones that failed on me were all over 5 yrs old as most of my sthil stuff was back ups .

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