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stihl ms660 won’t start

Discussion in 'Chainsaw' started by LetTheChipsFly, Mar 16, 2019.

  1. LetTheChipsFly

    LetTheChipsFly ArboristSite Lurker

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    gday from Australia fellas

    righto my problem started a couple days ago saw ran fine for about an hour and when it got hot it wouldn’t start up i’ve been through the basic stuff seems to be getting spark fine cleaned the carby although when pulled fuel floods out of the muffler i’ve taken a few photos of the piston what’s your thoughts
     

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  2. president

    president ArboristSite Guru

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    Check the inlet needle ,and passage in the metering chamber
    1 turn out for both high&low ,richer on high if muffler modded
    mabey choke plate sticking closed?
     
  3. LetTheChipsFly

    LetTheChipsFly ArboristSite Lurker

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    yeh what do you think about the piston
     
  4. brock1994

    brock1994 ArboristSite Operative

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    Straight gas would be my first guess. Then running to lean would be my second.

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  5. LetTheChipsFly

    LetTheChipsFly ArboristSite Lurker

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    so you think the piston is shot?
     
  6. brock1994

    brock1994 ArboristSite Operative

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    Oh for sure. The cylinder might clean up.

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  7. LetTheChipsFly

    LetTheChipsFly ArboristSite Lurker

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    Definitely hasn’t been straight gassed
     
  8. rmh3481

    rmh3481 Addicted to ArboristSite

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    Its hard to tell sometimes by looking thru the exhaust port. Ive seen worse run well. A scuff on the skirt that doesnt run up through the ring lands is usually nothing to worry about. I do see other marks around the top of the piston, so at this point its about the cylinder. Has it been rebuilt before? Chin Parts? I think you should run a compression test (psi) on it and then go from there. If its new to you and had an offshore piston put in it for sale, I think you know whats up.
     
  9. lone wolf

    lone wolf MS 200T King

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    Definitely damaged rip it down. If It was mine I would put new seals, hoses,and piston also clean the cyl and do a vac test. No China stuff in there!
     
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  10. brock1994

    brock1994 ArboristSite Operative

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    Maybe it was running to rich and excess carbon build up fell off the combustion chamber and caused the scoring on the piston. Like everyone said I would pressure and vac test and then go from there. Definitely needs new piston and rings at very least. Good luck hopefully you figure it out.

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  11. LetTheChipsFly

    LetTheChipsFly ArboristSite Lurker

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    closer look at the cylinder
     

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  12. LetTheChipsFly

    LetTheChipsFly ArboristSite Lurker

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    closer look at the piston
     

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  13. drf255

    drf255 BAD CAD

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    Chi-wan-Eeze Cylinder?

    Your missing some plating there. I woulda thought your piston was ok to run, honestly.

    It’s good you tore it down.

    If the saw still had plenty of compression, I was gonna say to check the coil after changing the spark plug. No spark will flood a saw up as well.
     
  14. Ando81

    Ando81 ArboristSite Member

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    Hi mate, another Aussie here trying to share some things I’ve learnt. Is the cylinder stamped with Stihl on it somewhere? I’ve heard that Chinese cylinders can have a sharp edge on them at the ports and can cause them to grab the ring on the way past if the carby leans out. Saying that, I bought my Jonsered 2165 with piston damage like this and it wouldn’t start. I pulled it down and cleaned the piston, rings & cylinder up so it was free of aluminium again. It now runs fine and hasn’t let me down yet. My saw had more damage on the piston to the extent that the ring was stuck to the side of the piston and had to be persuaded to come free from the piston. I’d try cleaning it up carefully first and assemble it to do a compression test, making sure that the ring gap isn’t lined up on the skirt like in your photo. I’ve heard that it’s not ideal to have the ring gap in line with the skirt. Good luck mate
     
  15. LetTheChipsFly

    LetTheChipsFly ArboristSite Lurker

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    yeh after having a good look at it the cylinder definetly isn’t OEM ive binned it and ordered a genuine one already along with a new spark plug coil and a new walbro carby i picked it up dirt cheap so expected some issues only thing i never did was run a compression test before pulling it all apart so hopefully there’s no other dramas
     
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  16. Ando81

    Ando81 ArboristSite Member

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    Yeah it’s probably going to be a lot more reliable to have high quality parts put back into it. I’d rather do it right the first time than always be doubting its reliability.
     
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  17. LetTheChipsFly

    LetTheChipsFly ArboristSite Lurker

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    yeh mate don’t wanna stuff around with crap parts i don’t run any on all of my saws old mate i picked it up from said he had the cylinder and piston replaced not long before i picked it up off him so im still not 100% sure it’s the main issue i got it cheap so either way at the end of the day it’s gunna be a reliable saw that doesn’t owe me more than it should
     
  18. Ando81

    Ando81 ArboristSite Member

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    I’d be making the carb run a bit richer to be safe as a starting point. Don’t want to risk a new piston if someone has set the carb to run lean
     
  19. Gord404

    Gord404 ArboristSite Operative

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    Fixed a 660 a while back, gas flooding when hot and yours probably got good and hot, because of the tank breather that is one way in and won't let pressure out your carb has to hold the pressor back and if its getting past the needle, well floods the engine, at the least it needs a carb rebuild and a new top end and a vac- press test when all is said and done.
     

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