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Stumped by Stihl MS391 Chainsaw

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    Stumped by Stihl MS391 Chainsaw

    Gents,

    I am usually pretty mechanically inclined but this one has me stumped.

    Stihl MS 391 chainsaw
    Let my buddy borrow it for a couple months and he used it often and without any issues.
    I get it back and put recently fresh gas in it.
    Started it and it ran for about 15 seconds. Died. Won’t start back up.
    I am getting good spark.
    I am getting air.
    I am getting compression.
    I can spray starting fluid directly in the carb or directly in the cylinder without getting it to even turn over.

    I’m stumped. Thoughts on where to look?

    Thanks!

    #2
    Sorry I'm no help with a fix. When I try, I always end up with extra parts.

    Kudos to you generosity. I've had a firm rule my entire adult life. Do not lend your chain saw or girl friend to anyone - ever.

    Sent from my SAMSUNG-SM-G930A using Tapatalk

    Comment


      #3
      Sounds like the jet may have something in it or the float is stuck. Take carb apart and inspect.

      Comment


        #4
        Have you pulled the cover off and tried to start it as usual and check for the choke to see if it opens back up? I’ve got an old Stihl that will hang up sometimes.

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          #5
          Try removing the muffler assembly and try to start. A clogged muffler can cause this. Then you may want to make sure you have a new plug. Next make sure the flywheel key is not sheared. One of the 3 are very possible the problem.

          Comment


            #6
            I had a small filter type in the gas tank of my 2002 ms290 that was replaced, was causing mine tot not start.

            Note taken: do not loan out the chain saw period.

            Comment


              #7
              Originally posted by TROOPER View Post
              Try removing the muffler assembly and try to start. A clogged muffler can cause this. Then you may want to make sure you have a new plug. Next make sure the flywheel key is not sheared. One of the 3 are very possible the problem.
              This

              Comment


                #8
                My son works on them and he said the flywheel key may have been sheard. Also said take spark arestor out of muffer( the screen).

                Comment


                  #9
                  Originally posted by Biggs View Post
                  I can spray starting fluid directly in the carb or directly in the cylinder without getting it to even turn over.
                  Sounds like a spark issue, either no spark at the plug or at the wrong time.

                  Comment


                    #10
                    Sounds like a timing (flywheel key) issue if you have fire and it will not start

                    Starter fluid in excess is not good for any kind of engine

                    I will go cut something up before I loan a chain saw

                    Wrong (straight) gas, sawing dirt, rocks, barb wire, etc

                    Comment


                      #11
                      I really don't think this issue has anything to do with someone borrowing my saw. I trust the man entirely. and he is good with tools and equipment. I think it is just a bad coincidence.


                      Originally posted by Reaper87 View Post
                      Sounds like the jet may have something in it or the float is stuck. Take carb apart and inspect.
                      I'm bypassing the carb by spraying directly into it and the cylinder.

                      Originally posted by Sleepy View Post
                      Have you pulled the cover off and tried to start it as usual and check for the choke to see if it opens back up? I’ve got an old Stihl that will hang up sometimes.
                      yes. choke is functioning.

                      Originally posted by TROOPER View Post
                      Try removing the muffler assembly and try to start. A clogged muffler can cause this. Then you may want to make sure you have a new plug. Next make sure the flywheel key is not sheared. One of the 3 are very possible the problem.
                      muffler might be a good idea. i had not thought about that far downstream. I have 3 new plugs just in case. I will have to look at the flywheel... I was assuming it was good because I am getting good spark.

                      Originally posted by tps7742 View Post
                      I had a small filter type in the gas tank of my 2002 ms290 that was replaced, was causing mine tot not start.

                      Note taken: do not loan out the chain saw period.
                      Bypassing the gas path by using starting fluid direct to carb or cylinder.

                      Originally posted by BTLowry View Post
                      Sounds like a timing (flywheel key) issue if you have fire and it will not start

                      Starter fluid in excess is not good for any kind of engine

                      I will go cut something up before I loan a chain saw

                      Wrong (straight) gas, sawing dirt, rocks, barb wire, etc
                      I will look at the flywheel key.

                      Comment


                        #12


                        Flywheel key looks good and intact?

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                          #13
                          I had an issue like this a long time ago. Had good spark it seemed. But
                          Like someone else mentioned at the wrong time. All I did was chance the plug and it was all good.

                          Comment


                            #14
                            Dumb Question, but is the relief valve closed? I think that model has a relief valve on the heads to make it easier to start.

                            Comment


                              #15
                              Got it! I can’t explain it but the return ground wire from the magneto was loose. So I was getting spark but... ????

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