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Stihl got the Blues...!

Discussion in 'Mechanic and Repair' started by AltaLawnCare, Jul 31, 2002.

  1. AltaLawnCare

    AltaLawnCare LawnSite Senior Member
    Messages: 961

    I've got Stihl problems. I have an old FS 80 trimmer, that when it gets hot - it wont take the gas, it just bogs and cuts off.

    My new FS85 is starting to do the same! It's not as bad as the FS80, I can still use it.

    The FS80, has had the following done to it so far...
    New plug, Muffler cleaned out, air cleaner cleaned, gas changed, fuel filter cleaned, carb kit installed, firing checked, new fuel lines installed.

    I run Amsoil 80 to one..(1/2 bottle to 2.5 gallons of gas)

    Next, I'm gonna try some stihl oil, just to see if the new one will straighten out before it dies too!

    Anyone have any ideas?? :confused:
  2. grasmo

    grasmo LawnSite Member
    from fl
    Messages: 34

    make sure the carb. idle and main circuits are adjusted, the fuel pump/needle tang is adjusted, and make sure you have a good cylinder.
  3. barnard

    barnard LawnSite Senior Member
    Messages: 618

    The next time you run it runit until it bogs, then loosen the gas cap and see if it makes any difference. It might be a vent problem . Air can't get in the tank-gas won't get in the carb.
  4. General Grounds

    General Grounds LawnSite Senior Member
    Messages: 902

    :blob3: gas cap all the way...
  5. olfrt

    olfrt LawnSite Member
    Messages: 48

    Assuming this just started suddenly

    When it is acting up check the spark to ensure that it is not a spark problem.

    hope this helps
  6. AltaLawnCare

    AltaLawnCare LawnSite Senior Member
    Messages: 961

    Thanks, everybody. ;)

    I hope its not a problem with Amsoil, I run it 80to1.

    I rarely go wide open, most of the time I'm 3/4 throttle, and just hold it there. The guy working on it for me said that might be a problem - hes a very good mechanic, but works as a automotive mechanic, not small engine.
  7. Jeff in AL

    Jeff in AL LawnSite Senior Member
    from Alabama
    Messages: 760

    On the older unit, it will most likely be the muffler or exhaust port starting to stop up with carbon. If so, it will need to be cleaned out.
    On the newer FS 80, I would check the coil. I have replaced probably 15 coils in the past 4 mo. Stihl has had a problem with some of the coils, and are now using a different manufacture for them.
    To check the coil, run the unit as normal (wide open throttle) for about five minutes, and then shut unit off. Then let it sit for two or three minutes and then restart it. If it starts, most likely its NOT the coil. However, it probably won't start. In this case the coil is bad and will need to be replaced.
    Here's the deal, while the engine is running, enough air passing over the engine is keeping the coil cool enough to work. When the engine is shut off, the engine temp. goes up for a short period of time, because there is no are blowing over the engine to cool it. While the engine is getting hotter after it has been shut off, there is a solder joint in the coil that breaks from the heat, and when the engine has had enough time to cool off, the solder joint makes connection again, and will run just fine untill the unit is shut off again.
    One more thing you can also do to verify this is to remove the top orange engine cover, and look at the coil. The coils that have had the problem have a CLEAR potting compound on the top of the coil, and the replacment, or the known good coils have a black potting compound.
    If the coil ends up being the problem, take it to your dealer, and they should replace it at NO charge to you.
    The part number for the coil is 4137 400 1350

    Hope this helps

  8. Clewsew

    Clewsew LawnSite Member
    Messages: 60

    I know that this is late, but maybe better late then never. I believe that the Sthil 2 stroke engines run 50-1 for the oil mixture. if you are running 80-1 then you are most likely running the engine lean on oil, which would cause overheating and eventually damage to your engine!

    Also, I have been told to run the engines is the best thing for them in keeping the muffler and screen from fouling(although I do not run WOT very ofter myself.) The 50-1 mixture is set to be optimum at WOT. Less then WOT causes the oil to be a richer mixture, causing fouling. In your case, your only running 3/4 throttle may have saved your engines.

    One last note, my FS85 manual says that after running the unit hard to let it idle for a couple of minutes before turning it off. This is because the engine turning does create airflow to help cool the engine off.

    Hope this helps,
  9. khouse

    khouse LawnSite Bronze Member
    Messages: 1,465

    I have ran Amsoil 100 to 1 since the late 70's. I have ran it in my Shindaiwa power head, Redmax trimmer, Stihl chain saws, Rm 125 Suzuki, lawnboy mowers. I have never had a major engine failure. It's been in a 1977 lawnboy since new. I'm sure at 80 to 1 your very safe. I do 3 lakes with the Redmax wide open for up to 4 hours strait. I would have to say the fuel cap,fuel filter or coil - in that order.
  10. AltaLawnCare

    AltaLawnCare LawnSite Senior Member
    Messages: 961

    Thanks everybody!

    The FS80 is still apart.. We think its sucking air around the carb to head mount, so I ordered a new gasket.

    The new FS85 acts up some, I've tried changing back to Stihl oil, but no difference, it just smokes more.

    I hadn't been letting it idle before shut down, I'll start doing that.

    The backpack is running good and its still on the amsoil. I'll probably take the FS85 in to the dealer when things slow down. The 85 will not run wide open, it just misses badly.

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