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90 HP Yamaha 2 Stroke 1988

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  • 90 HP Yamaha 2 Stroke 1988

    Hello,

    Can I please get some help identifying compression number on my 88 Yamaha 90 hp outboard. I just did a compression test with the motor warm and all plugs out. I got between 80 and 82 on all 3 cylinder. I understand that I am looking for all cylinders to be in the same range.My question is I have see used Yamaha 90 hp motors for sale that had number over 100? Could this be an issue? Not a ring but crank seal etc? The motor has been running very well and appears to have plenty of power mounted on a 17 ft Boston Whaler and moves it well. I have had to Boat for a few years and I do know the cylinder head was replaced but other than that I have kn knowledge of a rebuild or any other work. I just want to make sure if I have an issue lurking I can get a grab on it in the off season.Thank you for any help you can provide.

  • #2
    The test should be done with the throttle plates wide open.

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    • #3
      Yes throttle was open all the way I even bought a new compression gauge with the same results Battery was fully charged and motor was spinning fast. I am going to decarb and see if that helps but most number I have see for these motors are 120's.. Its strange because it is running good.

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