STIHL BG85C blower - carb removal

Discussion in 'Mechanic and Repair' started by Roger, Nov 10, 2011.

  1. Roger

    Roger LawnSite Fanatic
    Posts: 5,919

    My BG85 has started to degrade in performance and now does not run well enough to continue use. The pattern of "flameout," poor starting, and irregular power (fluctuations in rpms) tell me that the carb has degenerated diaphragms. It seems to me like it is not getting enough fuel. It is 6-7 years old, run daily for the season (mow/blow about 1,200 properties per season), and has been used hard for leaf work every Fall.

    I wanted to get a G & D kit, but need to know the Zama carb number. Like all STIHL products, the only way to get the numbers is when the carb is off and one can find the stamped numbers on the existing carb.

    When I went to take the carb off, I found the carb does not slip off the posts because of restraint by the throttle wire. It appears that the only way to slip the carb off the Z-connection at the end of the throttle wire is to rotate it, but this only can happen when the carb is off the posts. Sure, I can take a plier, or some tool, to bend the wire, but I am concerned about getting the wire out of shape, never to be fitted up right upon remount.

    The attached pics show the carb in the fitted position, then slipped down the posts to the extent allowed by the wire. The sliding down the posts is not far enough for the carb to be removed. I think it needs another 3/8" or so.

    I though that perhaps the posts could be unscrewed, removed, and then the carb would be free to rotate as necessary to get the Z-connection unhooked. But, even though the posts seem a bit loose to unscrew, they seem "hard" connected. Perhaps the end of the posts have an L-shape, engaging in a slot, and are not screwed into the engine head.

    I seemed to be at a "chicken-egg" stage. I can't get the carb off, so can't get the numbers to get a G & D kit.

    Anybody know how to resolve this dilemma?

    Pic 1 is the carb slid down the posts to the normal postion. Pic 2, 3 and 4 show the carb slid up the posts, with the throttle wire still engaged in the throttle.

    Thanks.

    P1470016.jpg

    P1470018.jpg

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    P1470021.jpg
     
  2. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    I've not operated on an 85, but here's one thing you may want to consider--try operating the throttle lever on the handle to the wide open position. This may allow a little extra carb movement on the mounting studs. Don't know it this will help but it's worth a shot.
     
  3. Roger

    Roger LawnSite Fanatic
    Posts: 5,919

    dutch, ... I understand what you are suggesting. But, I've done that already. "full throttle" position gives more length at the carb, but not enough for it to slide off the end of the posts.

    Thanks.
     
  4. Patriot Services

    Patriot Services LawnSite Fanatic
    Posts: 12,680

    Double nut the studs and remove them or vise grip and replace. I highly recommned a new carb over rebuild. Late model carbs just never seem to rebuild well.
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  5. Roger

    Roger LawnSite Fanatic
    Posts: 5,919

    Patriot, are you sure they are secured with a threaded fit to the block?

    I thought that to be the case. However, I did use a ViceGrip on the bare shaft. The post rocked back/forth over a couple of degrees, and was "loose." This is why I made my comment that they may be L-shaped ends, being trapped between the block between the carb and the block. A parts diagram would be very helpful to know for sure what the ends of these posts looked like.

    The block between the carb and the block is held in place with a couple of screws. However, access to them depends upon the carb being off first.
     
  6. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    Roger,

    Having not spent more than a minute looking at an 85, I'm not familiar at all with the throttle linkage from the handle. Possibly unhook linkage in handle assembly? Beyond that, I don't have much of a clue without having the blower on the workbench in front of me. On the other hand, manufacturers(design engineers) do some stupid stuff from time to time.

    Maybe there's some secret that an authorized Stihl mechanic will share with you. It's too bad that Stihl doesn't want the consumer to have a look at a parts breakdown as they are sometimes helpful.
     
  7. Roger

    Roger LawnSite Fanatic
    Posts: 5,919

    Bingo!!! This facet of Stihl is very frustrating to me.
     
  8. dutch1

    dutch1 LawnSite Silver Member
    from Jayhawk
    Posts: 2,231

    That's one of several reasons I use and own Shindiawa equipment. I haven't seen enough of their equipment since the Echo/Shindiawa merger to determine if the quality/performance has changed.
     
  9. Patriot Services

    Patriot Services LawnSite Fanatic
    Posts: 12,680

    I'm going from 20 year ago mental image. You should be able to squeeze to full throttle, hold the blade full open, release the trigger and the cable end extends out of the retainer on the arm. God this is impossible to put in words. Its kind of unversal to most brands. The carb return spring pressure is what holds the cable in the slot.
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  10. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Posts: 1,164

    Remove the remaining screws from the handle half/grip and you will be able to remove the throttle wire and then pull the carb without having to remove anything else. I would not rebuild a carb with that age and amount of use. Also consider replacing the fuel hose assembly and fuel stone at this time.
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