Stihl BG 85 Blower Problem

Discussion in 'Mechanic and Repair' started by jud149, Aug 30, 2011.

  1. jud149

    jud149 LawnSite Member
    Messages: 102

    The machine starts fine but when you give it gas, it will die. After I continue to start it attempting to get it to run, it will after several starts run fine. Then after using it for 15 minutes or so, during which time it runs fine, the same problem will emerge after I shut it down and restart it. I've rebuilt the carb, replaced the fuel filter, and made sure the flame arrestor screen is clean, all to no avail. The unit has about 60 hours on it and this has been happening for some time but seems to be getting worse.
  2. 2stroked

    2stroked LawnSite Senior Member
    Messages: 296

    Make sure the gas cap is venting. Take the cap off and see if it runs well
  3. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    These are merely listed in order of expense from least to most expensive,
    in my opinion it could be any one of them.

    1. HI speed adjustment screw not open far enough, this screw needs to be open at least 3/4 turn from fully closed.
    2. Primer bulb cracked or corroded, if you can no longer see through it replace with a new one.
    3. Ignition coil.
  4. jud149

    jud149 LawnSite Member
    Messages: 102

    Well, I checked everything suggested here and the only thing that seems to help is to adjust the high speed adjustment carb screw two full turns out, which is much more than suggested by Stihl, I believe. In any event, it was running fine after I did this but I won't know for sure if the problem is solved until I use it again. Thanks for the help.
  5. jud149

    jud149 LawnSite Member
    Messages: 102

    Still having the same problem. I did notice that there is no fuel in the primer bulb when the engine is running. Is this correct?
  6. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Messages: 2,248

    You may want to pull the fuel line assembly and check for pin holes/cracks in the fuel line, both inside and outside the tank. I've had two 55's recently, one with cracked fuel line just above the tank bushing and one just inside the tank. No guarantee that this is your problem but it might be worth checking.

    It's been a while since I've seen an 85 but there should be two ports on the carb, a supply line and a return line. You may want to pull the return side, then prime to make sure you're getting fuel through the carb. Normally, there will be some fuel retained in the primer bulb while the unit is running.
  7. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    This has been the solution for me more than once, HI speed open way past 3/4's.
    Can't say this will always fix your problem, but it certainly falls under one of my things to try when all else fails.

    If you can no longer see through the primer bulb and it shows wear and corrosion (such as feeling rough to the touch) it may need replacing,
    when the rubber becomes brittle it is possible for it to leak and when that happens the engine tends to suck air.

    However, this usually also results in fuel leaks when the equipment is left sitting in anything but the perfect upright position,
    of course it's not always the case but that's another sign the bulb may need replacing is when the equipment leaks fuel.

    Either way it's a cheap fix, about $2, $3 for the bulb.

    Hope that helps.
  8. jud149

    jud149 LawnSite Member
    Messages: 102

    Thanks for the input. The bulb is new so I guess that rules that out.
  9. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    When I am not sure what the problem could be exact, my process of troubleshooting involves a series of steps that covers inspecting and replacing
    the cheapest thing(s) and gradually moving from that on to those things that cost more, and more...
    The reason why this works is there are only so many things that don't cost a whole lot to fix, and I figure it is always
    worth checking those first even if I don't think it could be the cause of the problem, sometimes it involves replacing things
    no questions asked, again it's about starting with the cheapest and methodically moving on up.

    Things such as spark plug, air filter, fuel filter, primer bulb.
    Yes, even if the spark plug was just replaced three weeks ago, it may not be the first thing I would do, but I'd likely still at least try to get to it.
    And if the machine still doesn't run by the time all that has been replaced, we're still only out a $20 and at least now some
    to most of the periodic maintenance has been taken care of, it is one way I can keep up with these things because in my
    old age I sure seem to fall behind on the maintenance something awful and the reason why I am explaining this is because
    that is how I fix my own machines.

    Does it always work, no, at times this can also be frustrating but it is the way I do things, and that is all it is.

    If what I have told you doesn't, or hasn't fixed the problem...
    Then it's time to move on to more expensive stuff and in that sense I would certainly recommend
    following along what some of the other guys said, stuff along the lines of fuel lines and all of that.

    Good luck
    Last edited: Sep 7, 2011

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