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BR550 Issues

Discussion in 'Ask the Experts' started by Roger, Oct 3, 2017.

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  1. Stump Shot

    Stump Shot Old *pretty boy dipstick of Quality

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    That would be helpful, hard to tell everything on the forum here.
     
  2. Roger

    Roger New OPE Member

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    Wolf, I'm a EE. Been using Fluke meters almost my entire life, and used one to make this measurement. You had it set up correctly. The only wild card is a defective meter. I had mine on an auto scale just like you, and they largely agree. The only exception is the wildly different coil tap to plug wire measurement. The first thing I'm going to do when the new coil arrives is make that measurement again.
     
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  3. Lone Wolf

    Lone Wolf Pinnacle OPE Member

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    Cant wait! The more I think about it if it was the coil bad it would run good then change if carb it would be more constant. OEM coil only!
     
    Last edited: Oct 8, 2017
  4. Roger

    Roger New OPE Member

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    Gentlemen, my blower is back!

    Short version:
    Today, my lovely wife ventured to the local Stihl dealer and acquired a new coil. After I got home from work I dropped it in, and it ran without looking back. In the dark I ran it though its paces on the leaves in the backyard without any hesitations or stuttering. I could kill and restart it at will without difficulty. It frankly has not run this well in years, which leads me to believe that the coil failure was a process, not an event.

    Longer version:
    The first thing I did upon arriving home was to measure resistance on the old and new coils, coil tap to plug wire:

    New: 1.7 MΩ
    Old: 20.4 kΩ

    I discovered that two Post-It notes stuck together and adhered to the flywheel provides a shim spacing of 0.203 mm versus the 0.2 mm spec. This made the job of installing it a breeze. Now a confession. I'm a cheap guy. After my last post on Saturday I ordered an aftermarket coil, $13 including shipping. Then Wolf posted to be sure to use an OEM part. After reading that I figured that if I ignored his advice, went cheap, and it didn't work, I'd have done him a disservice. You guys, and especially Wolf, deserve an accurate accounting of this fix, so I spent $48 for the OEM coil. Further, the aftermarket part won't arrive until Oct 18, so better to get this resolved sooner than later.

    The only problem I have is that the beast doesn't idle very well. RPMs way too low at idle after warm-up, and the idle adjustment screw is at its limit. I suspect (hat tip to Wolf) that this is because of my aftermarket carb. At some point I'll throw the original back in and I suspect I'll be golden.

    But I still have the aftermarket coil coming. When it arrives, and after the heavy leaf-blowing events are finished, I plan to throw that one in just to see what happens. I'll post that result and the carb swap when I do.

    I think it was Mark Twain who said that it ain't what we don't know that gets us into trouble. What gets us into trouble is what we know for certain that just ain't true. Man, if he was watching me wrestle with this thing over the last eight weeks, he's laughing his arse off. A dry plug means no fuel, right? Gotta be. Well, perhaps not on this engine. Or perhaps I had a spark that was strong enough to burn the gas off the plug, but not enough for combustion. Whatever. File this under the very long list of bad assumptions I've made over the years.

    Finally, it bears repeating. You guys have been great. Like I said earlier, my initial post on this forum was a flier. I really didn't expect any actionable responses, if I received any at all. Instead I found myself immersed in a think tank of great suggestions coupled with sound troubleshooting logic. I can't say I wouldn't have stumbled on the coil by myself, but you guys got me there much faster.

    Thanks again to all.
     
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  5. Lone Wolf

    Lone Wolf Pinnacle OPE Member

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    And faster than I thought ! Just shows that coils can in most cases be checked with an ohm meter. I am glad you got it going I know how it feels.
     
  6. Stump Shot

    Stump Shot Old *pretty boy dipstick of Quality

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    Glad you got up and running again, now go blow you some leaves!
     
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  7. tp2177

    tp2177 Super OPE Member

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    This thread reminds me that I need to go blow some leaves since the tropical storm just came through. Oh well my echo backpack blower needs a workout too


    Sent from my iPhone using Tapatalk Pro
     
  8. AVB

    AVB Well-Known OPE Member

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    Then basically you had an insulation breakdown. If you read the HV lead and the laminates you probably will discover that it has a lower reading too as some its winding are probably shorted together.

    Most times the High voltage (secondary) is check from the laminations with both sides of the transformer is grounded to at one end of the windings. The primary is usually has a very low impedance due to the trigger inductor (small transformer is these since the magnets acts as it primary winding through magnetic coupling). Checking the way you did is a good test for checking for shorts between the two sides of the transformer.

    Here is a basic diagram of how these coils are wired inside. These coils are more complicated today due the additional electronics that add spark advance and rpm limiters. You will notice that the secondary has no attachment on one end but this where the plug wire (high tension lead) is attached and the plug completes the circuits as it arcs to ground.
    [​IMG]
     
    Last edited: Oct 10, 2017
  9. Roger

    Roger New OPE Member

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    Thanks for this. I suspect more is going on inside these coils. My research indicates that the coil is processor-based to provide automatic timing adjustments. However, I think you're spot-on regarding insulation breakdown as my basic problem.
     
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  10. Roger

    Roger New OPE Member

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    WRAP UP

    Stihl BR 550 Blower Symptoms:
    1. When cold, blower starts on second pull every time, and runs great for a minute or two, then dies like either fuel or spark was shut down.
    2. Repeated attempts to restart are futile. Engine won't even attempt to turn over.
    3. Wait about 10 minutes and items 1&2 repeat.
    4. Pull plug after multiple attempts to start the blower. Plug is dry.
    5. Spray fuel down the carb throat, engine springs to life only to die again a minute or so later.
    6. Sometimes engine runs reasonably well for a longer time, only to sputter and die
    7. When checked, plug is always dry.
    8. Same symptoms with fuel cap off, eliminating possible tank vent issues.
    9. Spark check shows a white-color able to arc at least 0.25 inches.

    Erroneous diagnosis:
    1. Fuel delivery problem.
    Attempted repairs to no avail:
    1. Replace fuel lines, filter, and primer bulb.
    2. Rebuild carb
    3. Replace carb
    4. Adjusted valve lash
    Final resolution:
    It was suggested to measure coil resistance and compare with a known good. A measurement of mine from the coil tap to the plug wire was 20 kΩ. Measurement of a known good was 2 MΩ. I replaced the coil and the engine runs like new.

    P.S. Use only OEM parts. I replaced the carb with an aftermarket "equivalent." With a good coil engine idled high and could not be adjusted. Also, the throttle/choke cam does not operate properly. Actually, it doesn't work at all. Finally, while removing the aftermarket carb to replace the with rebuilt OEM part, the brass main fuel feed popped out of the carb body. This part is junk. Ditto for aftermarket coils. I bought one for $13 including shipping. It won't physically mount on the engine. And, in case you're as cynical as I am, I don't work for Stihl or a Stihl dealer!

    Thanks again to all on this forum who helped get this thing running in the nick of time. Leaves are falling like rain as I write this.
     
    Last edited: Oct 15, 2017 at 2:01 PM
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  11. Lone Wolf

    Lone Wolf Pinnacle OPE Member

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    :beer-toast1:
     
  12. AVB

    AVB Well-Known OPE Member

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    Had the same problems with the Ripbay stuff. I even been having problems with my regular after market supplier this year. Mostly belts the wrong lengths but I did just went though 6 MTD aftermarket spindles that made wrong. Finally had to get a drill press and drill out the broken bolts and rebuild the original spindles. Just had to source the taper bearings and seals. Any way it was easier to rebuild the original spindles than the hassles I went through getting the replacement spindles.
     
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