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Stihl SH85 leaf blower help

Discussion in 'Chainsaw' started by Streblerm, Nov 10, 2007.

  1. Streblerm

    Streblerm Addicted to ArboristSite

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    Ok, I know it isn't a chainsaw, but I thought some of the helpful folks at ArboristSite may have run into a few of these things.

    My problem is poor midrange and nonexistant idle. Once you get it to full throttle, It runs OK, but it doesn't seem to run like it should. No matter what I do with the "L D" screw it runs the same. It idles for about three seconds, idles up a bit, then dies. If I understand this carb, turning the screw clockwise richens and counterclockwise leans idle. There are no other adjustments on this carb.

    I have inspected the piston and bore and it is clean as a whistle, no scoring. I replaced the fuel line and filter with the new green one. I have had the carburetor apart multiple times and it looks clean. I have pressure and vacuum tested it and it passes. New air filter. New tank vent.

    No matter what I do to this thing, it runs the same. I have used it personally for about 6 or seven years. It has been running this way for about 3 years. I use it regularly, year round. I don't use it for long periods of time however. I suspect it has under 100 hrs of use.

    At this point, I am looking to replace the carb with something adjustable. No matter what i do with this thing, the plug reads slightly lean, at all RPMs

    Am I missing something here? This thing is making me doubt my mechanical ability.
     
  2. newguy18

    newguy18 Banned

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    Its hard to tell with out actually seeing it.I would try setting the needle at 1 and a half turns out after it was turned all the way in.i know you said it passed a vacuum test but maybe rebuild the carb.
     
  3. Fish

    Fish Account Hold

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    Remove the carb again, take out the spring/lever/needle , and hold up to a light and look through the hole, it is likely mostly clogged, blow it out and
    verify it is clear.
    The old cracked fuel line lets crud in the carb, as well as fine crud and scum
    gets past the fuel filter.
     
  4. Lakeside53

    Lakeside53 Stihl Wrenching

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    Pull the exhaust screen out and see if it's plugged.

    If yor fuel line is NOT green, replace it anyhow.
     
  5. Streblerm

    Streblerm Addicted to ArboristSite

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    Any problems with soaking in cleaner or using compressed air?

    I swear this thing is clean inside, But I'll take it apart again. Anybody know off hand if I can soak this thing in carb cleaner and blow it out with compressed air? Once I have the diaphragms out.

    Fish-Are you talking about the throttle shaft/return spring, and "L D" needle?
     
  6. newguy18

    newguy18 Banned

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    You can soak it and blow it out with compressed air.
     
  7. Streblerm

    Streblerm Addicted to ArboristSite

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    The exhaust screen is clean.

    I disassembled the carb again. The idle jet is fixed. If I shoot brake cleaner through the jet, It comes out the holes in the venturi. I can't believe it would be plugged. This thing is spotless inside.

    Can somebody explain the function of the "L D" screw? It has reverse threads so turning clockwise opens the screw. It isn't a needle. It is a broad screw that covers a hole in the venturi on the engine side of the butterfly. This must be air metering, Right? The fixed idle jet meters fuel through the three small holes in the venturi on closed and partial throttle opening. The position of the LD screw provide extra air at closed throttle.

    Last year I even popped the welch plugs out and soaked it in carb cleaner. Could this have caused a problem? It really seems to me that the idle circuit in this carb just isn't working. An air leak should have caused it to blow long ago.
     
  8. Fish

    Fish Account Hold

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    Have you removed the metering lever/needle/spring, it closes a hole
    that goes to the otherside, to a hole under the small screen on the the
    fuel pump side, that hole must be clear, hold it up to the light.
     
  9. Streblerm

    Streblerm Addicted to ArboristSite

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    Yes, all clear.
     
  10. newguy18

    newguy18 Banned

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    when you rplaced the welch plugs you didn't by chance try to seal them?i know it sounds stupid but I had a man bring me a chainsaw that he had rebuilt the carb on and could'nt make it run and it turns out that he tried to use rtv sealant on the welch plugs.
     
  11. Streblerm

    Streblerm Addicted to ArboristSite

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    Nope, no sealant on the welch plugs.

    I'm so frustrated with this thing, I think I'm just going to keep running it till it blows. It starts like a champ, and runs fine at WOT. It just won't idle for more than 5 or 10 seconds.

    Good thing it has cruise control.
     
  12. jack-the-ripper

    jack-the-ripper AboristSite Guru

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    The "LD" is the idle speed screw. When the engine is warmed up, turn in counterclockwise gently to seat (left handed threads). Then out 2 full turns clockwise. This is the standard factory setting. If it doesnt idle right after that, about a half turn clockwise until it idles smoothly.

    I have the BG85. It has the "LA" for the idle screw also the high and low speed adjustments. The info is per the owners manual.
     
  13. Lakeside53

    Lakeside53 Stihl Wrenching

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    The LD in this case is an air bypass screw - the fuel is fixed and you are varying the air.
     
  14. jack-the-ripper

    jack-the-ripper AboristSite Guru

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    These images are right out of the owners manual. Sorry they aren't smaller.



    [​IMG][​IMG]
     
  15. Kogafortwo

    Kogafortwo AboristSite Guru

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    Been there - feel for ya

    I've been working on my old BG72 for several weekends in a row. Today I replaced the head gasket, flywheel-side crank seal, and tried readjusting the needle lever either side of the spec, all this after rebuilding the carb TWICE.

    I went through all the same stuff you did - checked the obvious holes and leaks and blockages, blew everything out, etc etc. Lots of good advice on this forum, especially from Lakeside, but I am now out many hours and a few bucks on a dead blower. I am ready to ditch this thing and buy a new BG55.

    I hope you have better luck!

    P.S. On a good note, at least my old beater 028 Wood Boss is screaming since I cleaned it and tuned it up a little bit yesterday.
     
  16. Streblerm

    Streblerm Addicted to ArboristSite

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    OK, so turning it clockwise (left hand threads) opens the screw and leans the idle by introducing more air when the throttle is closed. As you turn clockwise it reveals more of the air bypass hole.


    I appreciate the time you guys took to paraphrase and copy the owners manual info. I should have said that I have the owners manual. I just didn't understand exactly what the owner's manual was saying regarding lean/rich direction. The introduction of the left hand threads added another level of confusion in my tiny little pea brain.

    Anyway, thanks for the help all. As I said, I'm just gonna run her wide open till she pukes. I'm not spending any more money on this POS non adjustable EPA turd.

    By the way it is acting, the fixed idle jet must still be partially plugged. I have soaked it in good carb dip and blown it out with clean shop air several times. I can disassemble this thing with my eyes closed in less than 5 minutes.

    Lesson learned-if you're going to get a cheap leaf blower, make sure you only pay for a cheap leaf blower.
     
  17. Rleonard

    Rleonard ArboristSite Operative

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    I've had my SH85 for a couple of years now. I use it casually but frequently and it has always been reliable. If you bought it new you have at least $220 in it. there are few other machines that can do the same job, but they will cost you to get into them. What is the objection to springing for a new carb? At this stage it appears to be the cheapest option, other than living with the problem.

    Bob
     
  18. Streblerm

    Streblerm Addicted to ArboristSite

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    Well, I've had some degree of success. I decided to have another shot at cleaning the carb. I disassembled and soaked it for 24 hrs. I rinsed and baked the thing on my grill (the wife frowns upon cooking garage things in the kitchen) for an hour.

    Either there was some diaphragm behind the fixed idle jet, or rubber from the deteriorated fuel lines got through the fixed jet into the cavity behind it. Anyway, when I baked it some black tarry substance oozed out the idle jet. I cleaned it again with some fine wire, and now it isn't lean at idle anymore...

    Unfortunately, many zealous cleanings have taken their toll on the fixed jets as now it is running a tad rich.

    I guess I'll keep my eyes open for a replacement adjustable carb.
     
  19. newguy18

    newguy18 Banned

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    i used to live in akron so i don't know how close you are to a repair shop called streets mower in kenmore.It is on kenmore blvd also check out a stihl dealer called bath tractor.
     

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