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  1. #1

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    John Deere

    Stihl FS55 - No Start -- A stupmper

    OK... there like 1000 'no start' posts on various 2 cycles.. and I've read most, and still stumped... Here goes.

    FS55 trimmer... was working fine this summer, and then refused to start after being set aside a couple weeks. Here's what I did:

    A) Symptom -- no 'kicking' even with starting fluid.
    B) Check spark... nada. Switch worked, so replaced coil (stihl part), gapped to .010" , and now got good spark. New plug as well
    C) Check compression -- got 120psi. Inspected piston through exhaust port... no scoring, rings looked good.
    D) Checked flywheel... pulled, looked good, in keyed area, no looseness, put back together.
    E) Tried starting with a bit of gas in the spark plug hole; no kicking over.
    F) Starter fluid may give a one or two kicks, but nothing near running. Seems like a backfire now and then, but mostly nothing.

    So... got spark, compression, and nothing. I'd expect a little running with a squirt of fued or starter fluid directly down the intake, but nothing.

    Haven't messed with the carb, but doesn't seem like a fuel issue.

    And yes, checked the spark arrestor... not bad but cleaned and reinstalled.

    I'm about end of my options.

    I've even tried starting with a drill connected to the starter wheel (jury rigged but worked... nothing worked ... no 'catching').

    Help..!! Any ideas? This machine has been consistent running for the 10 or so years I had it.... now nothing..

  2. #2

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    Re: Stihl FS55 - No Start -- A stupmper

    I believe you already know to use Stihl two cycle oil & high test gas, at least 91 or 92 octane.

  3. #3

    Join Date
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    Re: Stihl FS55 - No Start -- A stupmper

    Is this a older 2cycle or the 4 mix?

  4. #4

    Join Date
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    Toro

    Re: Stihl FS55 - No Start -- A stupmper

    Have you checked the crankshaft seals on both the flywheel and PTO ends. If they are bad you are sucking air into the crankcase.
    This is only my opinion, and many will say it ain't worth a darn, as I'm only a retired grease monkey instructor and not a professional mechanic. Use what I post at your own risk as you know teachers only know book knowledge.

  5. #5

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    John Deere

    Re: Stihl FS55 - No Start -- A stupmper

    To answer some of the questions:

    A) This is a 2 cycle, 50:1 mix

    B) I have been using the same gas (regular unleaded + high quality oil) its whole life, and working adequately

    C) When I had the flywheel off, the shaft seal looked OK... no obvious sign of leakage. Would I still get good compression with a leaky shaft seal?

    Thanks for all the help... just looking for a direction to go... other than purchasing a new machine.

  6. #6

    Join Date
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    Re: Stihl FS55 - No Start -- A stupmper

    Two compressions on a 2 stroke.
    1) primary crankcase compression
    2) cylinder compression

    No connection between them

    A leaking seal is generally not visible to the eye
    If it is failing under vacuum as previously mentioned, air gets sucked into the crankcase so there will be no visual evidence of a leak.

    Crankcases get tested under both vacuum & compression.
    The dirty test is to put the piston at bottom dead centre , spray a little starter fluid into the plug hole then qhickly replace the plug and givee it a pull.
    Engine goes bang ( probably only once or twice ) indicates timing & secondary compression are OK
    Repeat by spraying into the carb with piston at TDC, A no fire indicates leaking seals.

    The follow up test is to put around a teaspoon of oil down the carb , piston tdc remove plug and pull vigerously with yout thumb lightly over the plug hole to stop air sucking into the engine .
    This will wet the seals with oil.
    Crank the engine again without your thumb to expel the excess oil.
    Use a NEW PLUG and try to start the engine as normal for it.
    If it starts & runs, worn seals are pretty well confirmed.

    The usual symptom of seals on the way out is an engine that is a bitch to start cold but once started will run & restart quite well.
    Leaking under vacuum will cause the engine to rev a lot faster at WFO .
    Most people do not notice this and will tell me "it has been running the best it ever has , then just stopped"
    This is because the lear burn causes the engine to rev faster then the cylinder wall runs out of oil and the rings score the bore.

  7. #7

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    Re: Stihl FS55 - No Start -- A stupmper

    Take the top off again, and the plug out, and rotate the engine to top dead center, then see where the magnets are in relation to the coil.
    Pewter Stihl Tech

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  8. #8

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    Re: Stihl FS55 - No Start -- A stupmper

    Or it could be just badly flooded, you might just dump the fuel and dry things out real well.
    Pewter Stihl Tech

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