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1977 175HP Black Max - poor accelleration and sometimes loosing prime

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  • 1977 175HP Black Max - poor accelleration and sometimes loosing prime

    Had the same poor accelleration issue last year. Replaced fuel pump kit and all carb gaskets in 2014. Then motor sat for 4 years. Fuel pump kit has maybe 2 hours of use since replaced in 2014. Starts fine, idles fine, accellerates sluggishly, but runs fine once it revs-up. Sometimes will stall during throttle-up. Must then squeeze primer bulb, then it will run and accellerate (but accellerate poorly - takes maybe a minute to finally get up to full rpm). I replaced the suction side of the gas hose (from bulb to tank barb fitting). two 6 gallon fuel tanks have vents open. Ran motor for for 3 hours off and on. Loaded onto trailer, tilted motor up, drove home 30 minutes. Pulled gas hoses off fuel pump pressure side (3-hose barb fitting which goes to 3 carbs) - no gas ran out. Pulled gas hose off fuel pump suction side - no gas ran out. Gas did run out of main gas hose when I lowered it toward ground (I guess gas siphoned out?)
    Could primer bulb check valve be allowing "leak down" letting gas to run backwards back into tank? Could BOTH 6 gallon tanks have bad O-rings in the barb-to-socket connection (I put some grease on the tank barb to see if it would "seal" a possible air leak at the tank barb fitting - no improvement was noticed).
    should I put a new fuel pump kit in (anyone know that fuel pump part number?)
    Also read that float levels are critical for good accelleration. I wouldn't think float level chanced mby itself but I will pull all carbs and check them if you think it's a good idea. (If I do what is the float level measurement (and measure from where to where?)
    Thnaks for your advice!!!

  • #2
    Ethanol gas will deteriorate fuel pump diaphragms and rubber fuel hoses even if engine has not been run so I would probably check them first. If you see any black or plastic looking debris in fuel filters then there is bad fuel hose, primer bulb or rubber components bad.
    Regards
    Boats.net
    Mercury Outboard Parts
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    • #3
      I have only used 100% pure gas (which happens to be Premium grade). I used pure-gas.org to locate ethanol free gasoline.
      I will replace the primer bulb and put in a fuel pump kit and check strainer.
      What fuel pump kit part number do I use for my 1977 Mercury 175HP serial 04733877
      Also please recommend a high quality primer bulb with 5/16" barbed ends

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      • #4
        On the longer fuel pumps then use kit number 89031A2.
        On the square fuel pumps use kit number 42990A10
        Use Mercury primer bulb, 8M0061876
        Regards
        Boats.net
        Mercury Outboard Parts
        MerCruiser Parts
        Force Outboard Parts
        Mariner Outboard Parts

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        • #5
          I ordered fuel pump kit 89031A2. Also ordered Mercury primer bulb 8M0061876 and new alcohol tolerant fuel line.
          Can someone send me a link that shows the sequence of gaskets and diaphragm in the fuel pump. Thanks!!

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          • #6
            The parts catalog is a good source for that, https://www.boats.net/catalog/mercur...-inline-filter
            Regards
            Boats.net
            Mercury Outboard Parts
            MerCruiser Parts
            Force Outboard Parts
            Mariner Outboard Parts

            Comment


            • #7
              Thanks for all your help!!!
              Does the Fuel Pump Kit 89031A2 include the check valve assembly #24 on exploded view (image 18887) Part# 30430A2. If not should I replace that as well?

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              • #8
                One last question (hopefully)
                Mounted on the gas tank, the "socket" (housing) that accepts the fuel line male barb adapter. This could be something like Mercury Part 83618M. There is a seal #92037 inside the housing "socket" that seals the tapered barb adapter as it twist locks onto the gas tank. I have the genuine Mercury 6-gallon tank and this SEAL #92037 is no longer available. Is this something I should replace too? Any suggestions on where to find this seal. I hate to have to throw away a genuine Mercury gas tank.
                PS I have two other aftermarket 6 gal gas tanks with an aftermarket female adapter and If necessary I can replace the whole female adapter BUT I have the same fuel starving issue no matter which gas tank I use.

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