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15 MSH missing in lower cycilinder

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  • #1

    15 MSH missing in lower cycilinder

    Thanks for the help nailing the year of my 15 horse down to '07...

    Now to the real problem I'm having. On cold start, the lower cylinder misses. Once the engine warms, it runs pretty well.

    The bottom plug fowls up.

    I have swapped plugs and coils. Replaced plugs with new. Checked the fuel pump for water and diaphragm integrity. Ran a quart of gas additive with PEA to clean the fuel system. Sprayed the carb with cleaner. Compression on both cylinders is good.

    Now take a look at the photo. Can anyone tell me what all that crusty white stuff is around the head gasket?

    Thanks in advance,
    You guys are great!
    Bry
    Attached Files
    Tags: None
  • #2
    Looks like the head may have been removed for some reason?...maybe head warped or not sealing properly?....a good bit of mineral/calcium deposits there at the gasket area...

    Comment

    • #3
      I've had the engine since new and the head has never been off. And the engine has never been dunked.
      Are you suggesting that cooling water is finding its way into the cylinder? The engine only runs rough and misses before it heats up. So if there is water in there, it dissipates soon after start-up and the engine runs normally.
      Further comment?
      And thank you,
      Bry

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      • #4
        Here' my lower plug.
        Attached Files

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        • #5
          How long did you run the motor to take the plug from new/clean to it's fouled condition?.... Is your fuel good and fresh?... Old degraded fuel can foul plugs.

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          • #6
            Boscoe
            can you repost that plug picture in a format I can open ?

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            • #7
              I run the motor daily and buy fuel every couple of weeks as needed. And it takes a couple of weeks for the plug to look as it does in the pix. The top plug is clean, nice tan color.

              I'll try to reformat the photo and send it along.

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              • #8
                see if this works for the pic

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                • #9
                  Hopefully/probably Rodbolt can give some ideas why just one plug would foul out like that....

                  Comment

                  • #10
                    My God

                    It's really simple and old stuff..If this is a four stroke,,more than likely its a intake valve guide that's worn and/or a broken/worn oil ring...why do you folk's here think that Yamaha came up with a new motor....Get a Grip !! nothing new and nothing awesome... same old sh-t..humans cant get past this old design

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                    • #11
                      Two stroke, two cylinder, one carb, pre-mix oil.

                      Comment

                      • #12
                        Originally posted by bajakeith View Post
                        It's really simple and old stuff..If this is a four stroke,,more than likely its a intake valve guide that's worn and/or a broken/worn oil ring...why do you folk's here think that Yamaha came up with a new motor....Get a Grip !! nothing new and nothing awesome... same old sh-t..humans cant get past this old design
                        If you would have read the OP 1st post it is a 2007 15MSH.
                        He said nothing about it being a F15 so we have to look at it as a 2 stroke, 2 cylinder , single carb with good compression and good spark.

                        If you can give some reason why only the bottom cylinder would foul it's plug he and some of the rest of us would appreciate the info you would care to give on that.

                        You Not reading the posts and bad mouthing people is not what he or any of use are looking for.

                        Hope the pic I posted is something Rod can see
                        Last edited by 99yam40; 01-19-2016, 03:45 PM.

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                        • #13
                          Originally posted by yammie15 View Post
                          Two stroke, two cylinder, one carb, pre-mix oil.
                          Must be something going on in that bottom cylinder to create a very rich mixture....carb jet, induction reeds, seals, bad gasket???..... Or maybe a weak spark causing poor combustion?....Hope Rodbolt will chime in here since he'll probably have some ideas on this....

                          Comment

                          • #14
                            Originally posted by bajakeith View Post
                            It's really simple and old stuff..If this is a four stroke,,more than likely its a intake valve guide that's worn and/or a broken/worn oil ring...why do you folk's here think that Yamaha came up with a new motor....Get a Grip !! nothing new and nothing awesome... same old sh-t..humans cant get past this old design
                            Having a bad day are we Keith? Hope it gets better for you.

                            Sarah Palin just endorsed The Donald for president. Wondering now if he has been nailin palin?

                            Comment

                            • #15
                              That's handy, she can organise hunting parties to collect animal skins instead of relying on road kill to cover ones head once Trumps trumps.
                              Your current candidates come across very poorly over here
                              Seems all you need is a sh....load of money, a crude load mouth and a crappy hairdo resembling roadkill to become favourite for president!

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