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Yamaha 150 idles rough/overfuels need help

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  • Yamaha 150 idles rough/overfuels need help

    Hoping someone on this board has some ideas and can answer some questions. I'm working on a 1987 or so Yamaha 150 ETXH. The engine idles rough, stalls, etc. It appears that it is overfueling because I can see and smell unburnt fuel coming out the exhaust into the water. It has fresh fuel and filter. Took a compression test, all cylinders ranged from 105 to 115. Checked timing at idle and was within spec at approx 6 degrees. Here's the kicker, looking at the 3 carbs, 2 have the numbers 6G403 stamped on them and the 3rd one on the bottom looks to be newer and has the numbers 6R20 stamped. Is that carb compatable to the other 2 and why is that number different. I don't know much on the history of this engine, just trying to get it to run correctly. Also, when it does idle it "coughs" and many times stalls or rpm dips way down. My next step would be to pull the carbs off but very concerned about the one carb having a different number. Anyone have any thought?

  • #2
    carbs probably need cleaning but DEFinately sounds like a bad fuel pump. the numbers should be different, hopefully they are the correct ones.

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    • #3
      same thing

      my 86 150 is running just like yours. did you find the problem? if so would you be kind enough to let me know what it was? my email is djs2nd@yahoo.com.

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