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    97 40hp Merc serial number isn't matching up with it's parts?

    Why not use the www.mercurypartsexpress.com website?
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    Need help

    Any idea as to the model of the motor?
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    '99 115 Yamaha choke butterfly plates are different

    Choke plates restrict the flow of air so as to increase the flow of fuel. Some have holes and some don't. I can't imagine the two different sized holes being a mistake. I am just guessing as to why they are different. But if if it is a manufacturing mistake then I will not argue against it.
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    '99 115 Yamaha choke butterfly plates are different

    Formula for the area of a circle is pi X r squared. Area of a 1/8" diameter circle is 0.012272 Area of a 1/2" diameter circle is 0.019635 The area of the larger hole is not even twice the area of the smaller hole. Not 5 times as large. Your first post said the choke plates with the smaller...
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    '99 115 Yamaha choke butterfly plates are different

    Depending upon their position I can see one set of carburetors allowing more or less fuel to flow. Which is why some carburetors use different idle and main jets. The carburetors with the smaller choke plate holes must need a bit more help drawing fuel into the carburetor when it is cold.
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    1999 Yamaha 115 idle adjustment

    The motor itself does not have an electric fuel pump. Or anything on the motor that would make a noise at key on. Perhaps someone added an electric fuel pump in the boat. Follow the fuel hose from the motor to the tank. See what is to be seen.
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    Low Compression, Low $ Advice

    There is a benefit to running pig rich. Less chance of leaning out a cylinder. Better to have rings with carbon build up than a seized piston.
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    High Pressure Pump OX66

    Having no idea which OX66 model you have, I cannot check to see what a Yamaha service manual says the pressure should be.
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    High Pressure Pump OX66

    The fuel pressure will vary. As a function of engine manifold pressure. Highest pressure at key on, engine off. A different pressure when the motor is running but at an idle. As the throttle is opened up the fuel pressure should go up. Throttle retarded the fuel pressure should come down.
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    Yamaha 2 stroke , shift cable adjustment ?

    No round decal with some numbers on it on the side of the block?
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    Low Compression, Low $ Advice

    What does that have to do with the OPs report of low compression?
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    Low Compression, Low $ Advice

    If it ain't broke I would not go fixing it.
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    Yamaha 2 stroke , shift cable adjustment ?

    The OX 66 models are oil injected with conventional fuel injection. The HPDI models are oil injected with direct injection. As noted, two different motor types. There is no throttle shifter sensor in either model. The throttle handle moves X number of degrees, after it has shifted into forward...
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    95 Mariner 4 stroke 9.9

    I believe that your carburetor also has an accelerator pump. Have you looked into the carburetor while rapidly advancing the throttle to see if a bit of gasoline is being sprayed into the throat of the carburetor?
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    95 Mariner 4 stroke 9.9

    There is no choke. Difficult to say how something that does not exist works.
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    Yamaha 40 hp 2 stroke tach hookup

    The rectifier/regulator has two green wires. One of which has two bullet connectors. One of those two are for a connection to a tachometer. For the RPM signal.
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    95 Mariner 4 stroke 9.9

    The cold start fuel enrichment component is what Yamaha calls a Primestart device. Mercury calls it a Primer Assembly. Allows extra gasoline to flow when the motor is cold. Progressively provides less extra gasoline as the motor warms up. When the carburetor was removed was it completely...
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    95 Mariner 4 stroke 9.9

    Any idea as to the complete model of the motor?
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    2004 mercury 90 four stroke EFI not charging

    Could be as simple as blown fuse, a bad connection point or it could that either the rectifier/regulator has failed or the lighting coil has failed. Do you have a multimeter and know how to use it?
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