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Yamaha 6A9 20cm. 2stroke (1980~) Difficult Idle problem

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  • Yamaha 6A9 20cm. 2stroke (1980~) Difficult Idle problem

    Hi everyone!

    I have had this problem for over a year , maybe 2 years.

    The problem is that when I start my yamaha it idles very rough. So little more gas ,and not rough anymore. Sometimes when its already warm I do the start and go ;D means that I put it in gear and then I start it so it will not die. When it starts and you have to put it in gear, usually it dies after 2 sec when in gear. When it idles it kind of do sound like "pok,pok,pok" and when it does The "pok" it kind of almost dies and then raises rpm and again "pok" till it finally dies. I have changed CDI, Spark plugs , ignition coil, head gasket and opened magneto but everything looked fine. I have cleaned carb 3 times ! Its impossible to reverse with this because it dies when Idle, and you cant floor the gas in reverse . But when I put it in gear and floor the gas, it will accelerate super quick ! Like it was never broken ;/. Idle is just very difficult to explain and to deal with .

    And Im sorry for my english, and its hard to write english with finnish mobile keyboard (autocorrects to finnish, damn it)

    Thank you everyone ! Have a nice day!!
    Greetings from
    Juho, Finland

  • #2
    sure sounds like a carb problem, but maybe the crankshaft seals are going bad and not sucking everything threw the carb.

    I would try a heated sonic clearer for cleaning the carb if you have not cleaned the carb with that in the past.
    hard to diagnose bad crank seals

    sure sounds like a lean sneeze happening


    • #3
      Has the carb ever been cleaned as far as you know?....I mean removed, disassembled and cleaned professionally, like 99yam40 mentioned...


      • #4
        Yes , The carb have been cleaned very well, believe me :/! And with heat Sonic cleaner. I've been thinking of the repair kit for the carb but everything looks just so good so havent yet bought anything.

        Yes it could be Crank seals. That's my not so biggest dream. ;D


        • #5
          Have you checked the fuel pump?


          • #6
            Fuel pump runs very good, I'm thinking that maybe just Bad Crank seals or Bad seals in carb. Honestly there might be 1000 different fixing ideas , haha!

            Maybe If carburetor just having very bad seals could be it, but they won't look bad at all. Although gasoline makes rubber seals to kind of swell up when they get old.

            Idle is just bad.

            I need to Look closer ..

            Thank you all for your time !