Stihl BG85 Blower erratic at WOT, sup carb. but......

Discussion in 'Mechanic and Repair' started by Henry101, May 17, 2019 at 10:52 PM.

  1. Henry101

    Henry101 LawnSite Member
    Messages: 24

    Hi,

    My dad has an older BG85 and it starts by the 3rd pull, idles fine, revs fine but when at WOT, it seems like it goes to full throttle for a few secs (sounds great) then it slightly revs down or maybe you could call it a slight bog. I have tried many different types of canned 50:1 mix, changed the plug, air filter, fuel filter and cleaned the exhaust screen. If you think it maybe a carb issue how would someone go about rebuilding one on a Stihl? I mean where do you get parts manual or service to reassemble the carb? I'm trying to learn about 2 cycle engines but scared to take carb apart without some sort of reference. It's almost twenty years old anyway, so I really don't want to throw a lot of money at it. Thanks!
     
  2. Walker56

    Walker56 LawnSite Fanatic
    Messages: 9,682

    Have you pulled the muffler and checked the exhaust port for carbon buildup? With a machine that old, your crankcase seals could be leaking which would effect your mixture. I think you need to do some more diagnosing. If it is determined that the carb is suspect, your carb should have numbers stamped on it. From what I see on the web, the carb should be a Zama C1Q. Here is the service manual. If this is not it, post your carb number.
    https://www.zamacarb.com/page/disassembly_servicing_1
    BTW, replacement carbs are somewhat inexpensive today. It really does not pay to rebuild
     
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  3. OP
    OP
    Henry101

    Henry101 LawnSite Member
    Messages: 24

    No I haven't pulled the muffler yet, I will try that next....Just need to get a gasket for it first. Thanks for the link BTW, a lot of good info! I was just thinking about rebuilding it for learning purposes and of course to fix the blower. The only occasion I use it for is for cleaning off roofs and gutters, just easier to throw on the backpack and easier on my hands. That's just me though, the BG85 doesn't have any anti-virbration on it, unlike the BG86. I will double check the carb number as I think it has been replaced about five years ago and check the port. Thanks for your help!
     
    hort101 likes this.
  4. BigFish

    BigFish LawnSite Platinum Member
    Messages: 4,991

    Look, Stihls very rarely clog the cyl. exh port. At any rate ya don't need a new gasket, the original one should stay intact, they always do fer me.
    Sounds like ya jes gotta tweek the HS mixture needle a bit. May have to carefully cut the limiter cap off with a pair of end cutters.
     
    hort101 likes this.
  5. OP
    OP
    Henry101

    Henry101 LawnSite Member
    Messages: 24

    Can you keep the limiter caps off or do they need to go back on the carb?
     
  6. BigFish

    BigFish LawnSite Platinum Member
    Messages: 4,991

    Leave them off. If the carb was replaced, it may not even have the limiters on it.
     
    hort101 likes this.

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