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YAMAHA 4HP 4 STROKE high idle when choke of.

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  • YAMAHA 4HP 4 STROKE high idle when choke of.

    hi wondering if you could help me i got my self a yamaha 4hp 4 stroke. and when choke is on it idles perfect however when i turn the choke of it idles very high .

    i cleaned the carb. however i not 100% sure how many turns main jet / idle jet need? does anyone know this info?

    also i been told to replace the intake gaskets ect for air leak ?


  • #2
    Sounds like an air leak causing a lean condition (which can cause the high idle issue.

    Turning on the choke is richening up the fuel mix bringing the A/F mix closer to where it should be..

    .
    Scott
    1997 Angler 204, Center Console powered by a 2006 Yamaha F150TXR

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    • #3
      if its like any other carb it should have a fast idle cam. sounds like even though the choke is open the fast idle cam is not dropping off to allow the throttle to close.. just a hunch.

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      • #4
        Originally posted by yamercury View Post
        if its like any other carb it should have a fast idle cam. sounds like even though the choke is open the fast idle cam is not dropping off to allow the throttle to close.. just a hunch.
        We don't know the year of the engine but I've never seen a fast idle cam set up on any Yamaha OB.

        Those were common on old school automotive, Rochester carbs, etc..


        With a year engine, the exact set up (carb) could be looked and verified..

        .
        Scott
        1997 Angler 204, Center Console powered by a 2006 Yamaha F150TXR

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        • #5
          Air leak or carb blockage, clean carb again, properly this time, check all mounting gaskets/seals for damage and go boating.

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          • #6
            Seem like if there is a choke, then there should be something that opens the throttle plates a little also.
            got to have air and fuel.
            but maybe not, the operator may need to crack the throttle open a little while choking

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