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Yamaha 6b issues

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  • #1

    Yamaha 6b issues

    Hey,
    My 1978 Yamaha 6b outboard (6hp 2 stroke)
    Has just started acting up, it runs great at idle but mid range it misses and jumps around. If you open the throttle flat it will rev up around half way and then you could wait maybe a minute (it varies a lot) and then it takes off up to full throttle and runs fine at that, but as soon as you let off it starts missing again.
    Just wondering has someone come across this before?
    I'm thinking it may be firing on one cylinder, maybe one coil on the way out?

    Fuel primer is hard,
    Fitted new spark plugs,
    Fuel mix is spot on,
    Tags: 2 stroke, yamaha 6b
  • #2
    Timing light hooked up to the plug wires will tell is they are getting spark while the miss is happening

    Comment

    • #3
      Originally posted by eoinyamaha View Post
      Hey,
      My 1978 Yamaha 6b outboard (6hp 2 stroke)
      Has just started acting up, it runs great at idle but mid range it misses and jumps around. If you open the throttle flat it will rev up around half way and then you could wait maybe a minute (it varies a lot) and then it takes off up to full throttle and runs fine at that, but as soon as you let off it starts missing again.
      Just wondering has someone come across this before?
      I'm thinking it may be firing on one cylinder, maybe one coil on the way out?

      Fuel primer is hard,
      Fitted new spark plugs,
      Fuel mix is spot on,
      It's also burning a lot more fuel than normal.

      Comment

      • #4
        Dirty / worn out carb. Possible leaking needle seat (thus the extra fuel).

        Peeking at your spark plugs may yield some information (fouled/clean, etc)

        If you have a timing light, put it over each plug wire while underway and see if the light goes out when the engine starts acting up.

        Eliminate or confirm an ignition issue..
        Scott
        1997 Angler 204, Center Console powered by a 2006 Yamaha F150TXR

        Comment

        • #5
          Originally posted by eoinyamaha View Post
          It's also burning a lot more fuel than normal.
          I know nothing about that small motor, but have you checked the fuel pump to see if it is leaking?

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