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Commercial series motor compression?

mik8881mik8881 Posts: 116 Deckhand
Do Yamaha Commercial (C) series motors have lower compression readings than standard motor ?


  • FS DanFS Dan Posts: 2,353 Moderator
    My old c85 was basically the same as the 90 without the oil injection and a different carb setup. measure each cylinder and see how they stack up against each other. should be all about the same or the bad one is usually easy to tell from the plug.
    Formerly Catmandew
  • mik8881mik8881 Posts: 116 Deckhand
    I tested with a cheapo harbor freight gauge all read 90psi on the dot no fluctuation in any . My concern was the 90 reading I read different reviews that 90 is acceptable others say it's low . I might add it was done on a cold start not sure how much of a difference that'll make .
  • FS DanFS Dan Posts: 2,353 Moderator
    sounds like your good then, no dead cylinders or stuck rings.
    cold start may have some effect but not much.
    Formerly Catmandew
  • Circle-HookCircle-Hook Posts: 503 Officer
    Did you have carbs fully open? that is proper proceedure and you should see 5 + psi increase
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