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I bought a stihl ms 660 chainsaw used with a 32 inch bar and chain. i ran it before i bought it and was good. then i started using it maybe 5-10 minutes and it died. i tried starting it again and took real long time and when it did start it didnt idle but died again. i took to repair shop and they said it was a scorched piston and cylinder. i paid $ 470 to get the piston and cylinder replaced. i was told by repairman to warm saw for about a minute before i go full throttle. i used the saw for about 3 tankfuls and the same thing happened again. i took back to repair shop and they said same thing happened and they are repairing it for free this time on the warranty. i use 89 octane fresh gasoline with ethanol, 50:1 oil mixture, and add fuel stabilizer. i was using echo synthetic blend oil and was told to use stihl high performance oil which i now do. what am i doing wrong? why is only one side of piston being scorched?

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They will score one side of the piston because of the heat.Its always on the exuast side.It could be the carb is adjusted to lean that makes it run hot.The muffler might need a good cleaning too?If it gets plugged up it will run hot too?It sounds like you gas and oil are mixed right.Thats about the only thing that will do it besides straight gas run in it.Could be the shop tec doesen't know how to adjust the carb?I would ask the to make sure its adjusted right.And not to lean.If its any kind of shop someone there should know how to do it right.When you get it back try running it wide open it should do whats called 4 stroke when not cutting wood then smoothe out while cutting.If you hold it about wide open and it runs fine.Its not right.If it does you need to open the high side of the carb a little.Maby a 1/4 turn at most.Just untill its getting to much gas to run smoothe.I hope they fix it right this time.Thats a very nice saw!

Posted on Mar 11, 2011

  • aheatseeker Mar 14, 2011

    thanks, ill try your advice. i bought the saw for $ 500 and thought it was a good deal but now im in it for 1000. brand new it goes for 1200. they are supposed to have it fixed beginning of this week. im dealing with the supposed best tech they have who went to stihl school. he is an older guy and seems to know what he is talking about. hard for me an amateur to tell him what to do. the previous owner said it was sitting in garage for past couple years. im thinking of also changing fuel line and carb and muffler to be on safe side. they had changed the fuel filter and put new gaskets on carb the first time. i really need the saw as i have a bunch of jobs to do and not much money until i do them. ill let you know what happens.

  • tbone75862 Mar 14, 2011

    You shouldn't need to replace the carb.The gaskets should fix it just fine.All long as the fuel lines are not hard or cracked they will be good also.The tech should clean out the muffler if he knows what hes doing.Sounds like he should.The muffler comes apart so he can clean the screen out.It will have some metal in it from blowing up twice I am sure.The screen is used for a spark arestor so it doesen't blow flames out of it.But it does have to be open for the saw to breathe right.Do let me know how its working.i will be glad to help best I can.



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