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Stihl BG55 Blower Problem!!!

Discussion in 'Mechanic and Repair' started by kptexan, May 1, 2008.

  1. kptexan

    kptexan LawnSite Member
    Posts: 15

    I will truly be thankful if you guys could give me some input on this annoying issue that I'm having with my Stihl BG55:

    My BG55 cranks up just fine after a couple pulls with the choke on and will run great across the entire rpm range when I initially start using the blower. After the first couple minutes of running, the blower will normally bog down briefly and then I let off the throttle. Once I reapply the throttle, I can normally bring the blower back up to full speed. The blower just seems to do this at random times. Often times I will have the blower under full throttle and then it will bog briefly and then come back up to speed. Occasionally it will do this several times in a row, almost like a random slow surge. At one time, I thought this issue was linked to something in the fuel system because when I would slightly tip the blower one way or another it would start or stop bogging down. When I was running the blower today I found that this was not the case because I set the blower on the concrete while at full throttle and it was still exhibiting this bogging surge behavior. My other thought is that it could be an ignition related problem once the ignition components get heated up.

    Here are the things that I've done to fix this issue but have had no luck:

    New mid octane fuel properly mixed with oil
    New spark plug
    New fuel filter
    New air filter
    Pulled out exhaust spark screen
    Checked lines running between tank and carb
    Adjusted carb to specs listed in manual (this made the blower run better but I still had the bogging issue)

    Do you guys have any other ideas? Maybe a carb rebuild or new ignition coil?

    Thanks so much for the help,

  2. ed2hess

    ed2hess LawnSite Fanatic
    Posts: 13,190

    I guess check to see if the exhaust port are clear....usually this unit don't clog...
  3. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    Yeh look in the manual on how to reset the L + H adjustment screws.
    Now if you do it wrong it will never run right again lol, but you can do it over until you get it right.
    Just be aware those stupid screws the heads wear off after so many times, so better if first try gets it.
    Far as I know you turn them all the way to the stop, then 3/4's turn the other way (just not sure which way to the stop).
    Also it might be diagrammed on the machine itself, right where the set screws are usually.

    Btw the 55 is a really nice blower, I have one thou I bought the flat tip nozzle for it...
    Then I just got me the 85, figuring it would be better.
    I am not impressed, it's a wee bit better but keep the 55!
  4. kptexan

    kptexan LawnSite Member
    Posts: 15

    Thanks for the quick replies!

    Yeah I set the L, H, and Idle Speed screws exactly as directed in the manual and, like I said, my BG55 ran better overall but did not fix my original problem.

    To check the exhaust port, do I just pull the two torx screws on the muffler and then pull the muffler off? If I remember correctly, those screws looked lock tited on.

    Any other ideas?


  5. 44DCNF

    44DCNF LawnSite Bronze Member
    Posts: 1,460

    It could probably use a fuel pump diaphragm.
  6. kptexan

    kptexan LawnSite Member
    Posts: 15

    So how would I go about changing the fuel pump diaphragm? Is this also part of a standard carb rebuild on these Stihls?

    I've been thinking that this could also be a fuel tank vent related issue so could that be a possibility?

    Also, is there a pdf version of some sort of Stihl factory service manual that I could reference to take things apart correctly? I'm quite mechanically inclined but I don't really like to just start taking things apart without some sort of instruction.

    Thanks so much,

  7. jkilov

    jkilov LawnSite Bronze Member
    from MS
    Posts: 1,415

    Yes, I`d definitively check this first.

    I think the BG55 has a ZAMA C1Q carb. Don`t know which variation.
    These are hard to rebuild. I suggest you buy a new one. You can then play with the old one and if you can get it fix, have a neat spare part always on hand.

    Here`s an IPL for the C1Q, it covers all serials, so your carb won`t have all the components listed here.

    Good luck.

  8. kptexan

    kptexan LawnSite Member
    Posts: 15

    Could someone please walk me through the steps of properly diagnosing the tank vent?

    Thanks so much,


    S DIAMOND LawnSite Member
    from South
    Posts: 108

    I believe the blower's vent is built into the fuel tank cap. When running the unit, wait till the same problem presents itself, and loosen the fuel cap. Does this improve anything? Usually when there's a problem with the vent (blockage), the unit will stop altogether, after 10 minutes or so. Underneath the fuel cap is a venting system with a "duck bill" check valve, a sintered filter, and a host of other parts. Before you embark on cleaning that, do the previous.

    Yes, this symptom is usually related to the carburetor and a weakening (brittle) diaphragm, or possible air leak.

    How old is this unit?
  10. rjxj

    rjxj LawnSite Member
    Posts: 80

    It probably has a separate vent. Its a black round plastic piece that pushes into a rubber grommet in the top of the fuel tank. Did you check the fuel lines real closely? They have a tendency to develop small cracks. They are black rubber. When you get the fuel line out, stretch it a little and look for cracks. The updated lines are green color and seem to be much better then the black ones.

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