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Stihl fs81 brushcutter

notnownotnow Member Posts: 1,858 ✭✭✭
edited July 2015 in General Discussion
It'll start and run for almost a minute then fizzle out and won't start at all. Rebuilt the carb. Same results. Checked the coil and sure enough it'll spark for a few pulls then nothing. Being an older machine, coils are between $75-$100. Here's the question, there's a small transistor unit of some kind mounted down under the engine case. Its involved with the ignition somehow. What does it do, how can I check it. This engine still has great compression. I'd hate to give upon it and I need one bad.
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Comments

  • notnownotnow Member Posts: 1,858 ✭✭✭
    edited November -1
    It'll start and run for almost a minute then fizzle out and won't start at all. Rebuilt the carb. Same results. Checked the coil and sure enough it'll spark for a few pulls then nothing. Being an older machine, coils are between $75-$100. Here's the question, there's a small transistor unit of some kind mounted down under the engine case. Its involved with the ignition somehow. What does it do, how can I check it.
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  • rufe-snowrufe-snow Member Posts: 18,650 ✭✭✭
    edited November -1
    You might consider transferring this question, to the General Discussion forum. Likely you would get more response, from the members that hang there. This forum deals specifically, with firearms related questions.
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  • charliemeyer007charliemeyer007 Member Posts: 6,572 ✭✭✭
    edited November -1
    My Sacks Dolmar 120 super chainsaw lost its spark. Brain box is like $300 if I could find one. I could add like $100 and buy a new saw that has parts available.
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  • notnownotnow Member Posts: 1,858 ✭✭✭
    edited November -1
    Thanks guys. I wondered if this was the right side to post this.
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  • MobuckMobuck Member Posts: 14,155 ✭✭✭✭
    edited November -1
    "Run for almost a minute" is a lot more than sparking for a few pulls. If you check it cold, it should spark for as long as you have strength to pull it since often the heat of running causes coil to stop sparking(or causes it to shortout and not fire plug).
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  • perry shooterperry shooter Member Posts: 17,105 ✭✭✭
    edited November -1
    I sell Stihl products a FS 81 is a much older unit than the type sold today. Now things are simpler when it comes to producing spark but I don't think you can retro fit any of the old units I am working tomorrow and I will try to get back to you
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  • WilyoteWilyote Member Posts: 32 ✭
    edited November -1
    There is an Arborist Forum some place on the web that helped me rebuild a few chain saws. If you are using ethanol gas in any equipment, it causes issues. The stuff leaves a residue when it evaporates which plugs the small orifices in the carb.
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  • pip5255pip5255 Member Posts: 1,625 ✭✭✭
    edited November -1
    have you tried a new plug, I recently had a plug doing same thing and I found it was defective, must have broken electrode internally because it doesn't spark all the time and is new, changed plug and works fine but it's not a stihl also.
    just because you could doesn't mean you should
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  • waltermoewaltermoe Member Posts: 2,394 ✭✭✭✭
    edited November -1
    Plugged up fuel screen.
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