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Stihl Hand Blower BG 55 Starts and idles fine but stalls out on WOT. Changed gas used Sea Foam.

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  • Gerald Gier Apr 09, 2011

    A friend of mine who works on engines told me the first thing I should do is remove some kind of screen at the muffler and throw it away. Also can you tell me how to identify the high speed and idle speed screws.

    Like which one is right and left looking at the carb.

  • Gerald Gier Apr 10, 2011

    Thanks so much...So often people provide an answer that doesn't address the question..You did well

  • John Van
    John Van Oct 18, 2013

    Mine doesn't have a low speed and high speed on it. Just one screw that says LD and it doesn't matter if you turn it or not. Still won't run when giving it gas. Sprayed carb and put new fuel line on. Nothing changes it.


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Hi and welcome to FixYa, I am Kelly.

You should first expose the carburetor and clean it with carb cleaner as best you can.
- Then as you turn the L screw jet clockwise cound the number of turns it takes to just barely stop turning and then remove the screw.
- Spray carb cleaner into the hole and then reinstall the L screw by first turning it all the way clockwise closed and then back it off the number of turns it took to close it to begin with. (Should be 1 & 1/4 to 1& 1/2 turns)
- Next close the H screw clockwise counting the number of turns it takes to just stop turning. Remove the screw jet by rotating CCW and spray carb cleaner into the hole.
- Reinstall the H jet by rotating clockwise until it just stops. Then back it off the number of turns it took to originally close it.

TEST engine.
Start the engine and make sure it is warm.
- Increase engine speed slowly until at medium range speed than try full throttle. If you have any hesitation at all adjust the L screw until the hesitation with a rapid speed increase stops. i.e let it idle... mash the throttle it should NOT hesitate if the adjustment is correct.
- Run the engine at full throttle. Adjust the H screw until maximum RPM is reached.
- Re test for hesitation from idle to full speed with a rapid cycle of the throttle. Make another L screw adjustment if necessary to get rid of the hesitation.

The Walbro manual is here:

The repair kit can be found here:

I do NOT recommend changing the Welch plug if you buy the repair kit unless it is severely corroded.

If after all of the above it is still stalling out with a WOT you will need to search for damaged fuel lines from the fuel tank to the carb and inspect the fuel pick up tube inside the fuel tank.
Hard or cracked fuel lines can cause havoc. If you have a fuel shut off make sure that it is free of debris.

Given your original symptom of stalling out at high speed only... you should just have to clean and adjust the H screw jet. Screw Jet adjustment: CCW = more fuel CW less fuel. Make the CCW adjustment until you obtain max RPM. Then check for hesitation from idle to MAX. If it hesitates... adjust the L screw turning not more than 1/8 th turn each adjustment until the hesitation from IDLE to MAX is gone.

Thanks for choosing FixYa.

Posted on Apr 09, 2011

  • Kelly
    Kelly Apr 09, 2011

    Hi again,

    As far as the screen being removed and thrown away it does serve a purpose and that is to provide some back pressure for proper air flow through the engine. What happens to the screen often is people use too much oil and it cakes up / blocks the exhaust port and the engine does not get enough fuel.

    The low screw is closest to the cylinder in front of the throttle plate / butterfly. And the high screw is closest to the air inlet or behind the throttle plate. (Page 4)

    Make sure your throttle plate is not loose and that it closes all the way to the idle screw stop when at idle. If it is not installed properly or got loose for any reason it will shift in the throat of the carb and prevent it from closing causing it to run fast.

    If by chance you have a fuel starvation problem it will briefly cause the engine to speed up but usually after the speed up peried the engine dies from a lack of fuel. The diaphragms in thes carbs can cause some weird symptoms... run fast, flooding, no idle, or no fuel. And if you install one upside down they do not work correctly either.


  • anthony AMATO Mar 25, 2013

    complete green horn - after my blower starts where do I move the throttle, as it runs for 60 seconds then kills


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