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I think I have a bad coil

Discussion in 'Chainsaw' started by cuinrearview, Apr 15, 2019.

  1. cuinrearview

    cuinrearview Red saw lover

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    It's no secret I like the 5100s and 5105 Dolmars. As many as I've had on my bench, I've never experienced the bad coils I hear talk of. I got the latest 5105 going tonight. Compression is good, good fuel, good spark. She tuned right in and responds beautifully. 2800 at idle, revs as quick as these do to 13.5k. Slapped a bar and chain on and went to the test log. As soon, and I mean as soon as it touches wood it loses everything. I lift it out of the "cut" and it returns to a smooth idle. Over and over. I tried it from cold and got maybe a second of cutting. It tried to run backwards a little and died. Fired back up and same.

    The flywheel is tight and on key. I only have one other coil, it's a red PS460 one though and looks pretty crusty. I got nothing from that.

    So, fellow Dolmar honks, is this what a bad coil acts like? If so, anybody got a spare black coil?
     
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  2. Dahmer

    Dahmer Addicted to ArboristSite

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    Are the kill switch connections tight?
     
  3. huskihl

    huskihl Addicted to ArboristSite

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    Is it the correct coil and flywheel? It sounds like it's advanced about 20° too far. The 5100 coils aren't compatible with the 5105 flywheel. And vice versa
     
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  4. huskihl

    huskihl Addicted to ArboristSite

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    Plug or ignition wire might be intermittently grounding out
     
  5. cuinrearview

    cuinrearview Red saw lover

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    No reason to believe the carpet doesn't match the drapes on this one. I thought of a couple sources for coils I can grab. The wiring all looks right. The coil is out right now so I can scrutinize the insulation later in the week. It's an easy start model so feeling too much advance is an impossibility, but running un-loaded everything feels spot on. Thanks for chiming in fellas. Sometimes you get into something and ignore possible solutions.
     
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  6. Old2stroke

    Old2stroke Never too many toys

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    Are you saying the engine actually ran backwards and fast enough to make the chain run backwards?
     
  7. cuinrearview

    cuinrearview Red saw lover

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    It returned to idle, the chain stopped, then moved a couple of links backwards. The chain is tight so it wasn't slack. I re-created it to make sure I actually saw what I thought I saw.
     
  8. Old2stroke

    Old2stroke Never too many toys

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    With normal ignition advance, an engine will not run backwards so if it does, something has changed to give no advance and the spark must be occureing at or near TDC. Modern coils are an ignition module with semiconductors that determine the advance, so that would be best guess for culprit. Last engine I saw that would actually run backwards was a Bultaco spanish trials bike, if it kicked back when starting chances are it was running backwards and you had to be real careful letting out the clutch. Ignition advance was purposly set close to TDC for low end power.
     
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  9. lone wolf

    lone wolf MS 200T King

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    If it runs at real low power I would say coil possibly. Swap it!
     
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  10. cuinrearview

    cuinrearview Red saw lover

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    Thanks for confirming my thoughts gentlemen. I remembered this morning I could probably grab my Dad's 5105 or open the box on my Makita to get a coil to try before i put up a want ad.
     
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  11. Old2stroke

    Old2stroke Never too many toys

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    Before blaming the coil, are you absolutely sure you don't have a fuel flow problem from the main jet? Restricted flow could let an engine rev up under no load but bog big time as soon as it's loaded. Wouldn't make an engine run backwards though.
     
  12. cuinrearview

    cuinrearview Red saw lover

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    Carb appeared fine when I had it apart yesterday. I have another to try if needed. I've experienced fuel related issues before, this seemed different and was what led me in the coil direction. The transition from running perfectly to absolute dogshit is so immediate.
     
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  13. cuinrearview

    cuinrearview Red saw lover

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    Update: I threw another used carb at it and a coil from my Dad's runner. Same outcome. I tested compression after that, so it was warm. I stopped pulling once it passed 155. I got my re-build kits from Definitive Dave yesterday, so I'll try re-building one of the carbs. I'm going to try a 5100s muffler after that in case the cat is plugged. Then a different fuel tank/line that I have laying around. After that I'll pull the clutch and see if there's anything in there.
     
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  14. lone wolf

    lone wolf MS 200T King

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    Well you put a known running coil on it right? Why don't you vac-press test the saw in the meanwhile. all you have to do is put the suspect carb on the other saw also!
     
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  15. cuinrearview

    cuinrearview Red saw lover

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    It has already passed p+v. I just assume people assume that that is done. I've got a fair amount of spares for this so swapping parts is easy. I also ordered the kits for both carbs. At $5 a kit I'll just do them both and have a spare ready to run. I just bought another junk one of these yesterday so I'm sure I'll use it.:)
     
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  16. Colt Marlington

    Colt Marlington ArboristSite Guru

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    Thought I had a bad coil on the 009L.
    It would start and run. But acted like it was getting hot real quick and wouldn't rev, then die and wouldn't start for a few minutes.
    Took the saw half way apart to pull the muffler and check the piston and cylinder, but all looked well.
    Caught CAD and went and got a bunch of other saws, and put the 009 on the shelf for several months.......

    Then finally decided to try a new spark plug to replace the one that looked perfectly fine...and now the saw runs perfect again.
     
  17. lone wolf

    lone wolf MS 200T King

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    Use a known tested runner!
     
  18. cuinrearview

    cuinrearview Red saw lover

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    A Denso W22 was the first thing I did...
     
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  19. cuinrearview

    cuinrearview Red saw lover

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    I can. And I might yet. I'm tempted to move on only because the exact same symptoms persisted. Hopefully my haste doesn't bite me in the azz...
     
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  20. cuinrearview

    cuinrearview Red saw lover

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    Gotta add, I love the way CCC packages their kits.
     

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