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Outboard only starts after manual priming of cylinders

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  • Outboard only starts after manual priming of cylinders

    Outboard only starts after manual priming as in pouring some fuel into the cylinders. Mercury 402 (year 1974)

    Ran perfectly after I did this last week, not sure why, Fuel pump rebuilt, Carb cleaned although hasn't been rebuilt, 99% sure that the fuel bowl was full. Compression check was good.

    Fuel does seem to want to be drawn beyond the bowl.

    Any advice greatly appreciated....
    Last edited by briaineo; July 30th, 2013, 06:39 AM.

  • #2
    Re: Outboard only starts after manual priming of cylinders

    The bowl may be full but the needle in item 6 may be sticking closed, preventing fuel from getting to the engine.

    Mercury, Mercruiser, Force, etc. - CARBURETOR ASSEMBLY - MERC 402

    As well, you have to ensure that the float heights are set correctly.

    Here is a link to the condensed version of the Clymer manual. Download it soonest to your computer as the link is short lived.

    http://web.ebscohost.com/serrc/pdfvi...3&vid=2&hid=23

    Gerry
    Last edited by carholme; July 30th, 2013, 08:13 AM. Reason: added link

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    • #3
      Re: Outboard only starts after manual priming of cylinders

      Make sure the choke is closing fully. These older Mercs like LOTS of choke on cold start-up and if there is any slop in the choke linkage, etc., it may not close all the way.
      [IMG2=JSON]{"data-align":"none","data-size":"full","src":"https:\/\/forums.iboats.com\/filedata\/fetch?id=9974593&d=1435747884&type=full"**[/IMG2]

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      • #4
        Re: Outboard only starts after manual priming of cylinders

        Originally posted by carholme View Post
        The bowl may be full but the needle in item 6 may be sticking closed, preventing fuel from getting to the engine.

        Mercury, Mercruiser, Force, etc. - CARBURETOR ASSEMBLY - MERC 402

        As well, you have to ensure that the float heights are set correctly.

        Here is a link to the condensed version of the Clymer manual. Download it soonest to your computer as the link is short lived.

        Gerry
        Hey Carholme

        I thought that the purpose of the needle was to stop the flow of fuel into the bowl when it gets full?

        Is the float adjustable? Was under the impression that it was not?

        thanks

        Eoin

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        • #5
          Re: Outboard only starts after manual priming of cylinders

          Originally posted by Chinewalker View Post
          Make sure the choke is closing fully. These older Mercs like LOTS of choke on cold start-up and if there is any slop in the choke linkage, etc., it may not close all the way.
          Hey Chinewalker

          I'll double check the choke, I was not aware that it could cause a fuel delivery failure. Is it a lack of suction the cause of the choke not aligning correclty?

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          • #6
            Re: Outboard only starts after manual priming of cylinders

            I added the link to the manual which I forget before. You will see the float height adjustment in there.

            Yes, the needle stops the fuel flow into the bowl when the float rises high enough. If it sticks there as it often does, you cannot get fuel into the bowl to be used by the engine. This is why you do a test by blowing into the fuel inlet line, and there should be full flow. Then you turn the carb upside down and blow again and there should be no flow. The tip of the needle produces a wear line over time and this causes it to hang in the seat when the float drops.

            Gerry

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            • #7
              Re: Outboard only starts after manual priming of cylinders

              Hey Gerry

              Thanks, I'll replace the needle tonight (and do the full carb rebuild) and check the float height, could you think of any other reason why the fuel might not get further than the bowl? Nearly certain the the bowl was full and the fuel didn't travel beyond that point!

              On that trying to figure out how it works: could you tell me the process in how the fuel gets sent to the cylinder for the initial start up, doesn't seem like an automotive carb the sprays fuel in on the movement of the throttle or should it?

              thanks

              Eoin

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              • #8
                Re: Outboard only starts after manual priming of cylinders

                DON T FORGET TO DOUBLE CHECK CHOKE OPERATION,you could be going crazy with carbs when all you needed was to repair choke operation,good luck john

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                • #9
                  Re: Outboard only starts after manual priming of cylinders

                  Originally posted by briaineo View Post
                  Hey Chinewalker

                  I'll double check the choke, I was not aware that it could cause a fuel delivery failure. Is it a lack of suction the cause of the choke not aligning correclty?
                  The choke richens the air-fuel mix to include more fuel, facilitating cold-start. The choke alignment has nothing to do with suction, rather it would be related to the bits that attach the choke to the solenoid and the manual choke lever. If the linkages get sloppy or if something is binding, the choke won't close all the way, if at all. Your statement that the motor ran well after you did get it started points to a choke issue...
                  Last edited by Chinewalker; July 31st, 2013, 12:54 PM.
                  [IMG2=JSON]{"data-align":"none","data-size":"full","src":"https:\/\/forums.iboats.com\/filedata\/fetch?id=9974593&d=1435747884&type=full"**[/IMG2]

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                  • #10
                    Re: Outboard only starts after manual priming of cylinders

                    My choke solenoid isn't connected at the moment, but do have the manual choke operational.

                    Replaced the needle and checked the adjustment of the float - all in line with the manual.

                    checked the operation of the primer bulb, seems fine,

                    Heard reed valves mentioned but was told once she run they should free up, which the motor did last week

                    Really stumped here....

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                    • #11
                      Re: Outboard only starts after manual priming of cylinders

                      Choke solenoid isn't connected. Does that mean you're manually operating the choke at cold start-up? Is it closing all the way?
                      [IMG2=JSON]{"data-align":"none","data-size":"full","src":"https:\/\/forums.iboats.com\/filedata\/fetch?id=9974593&d=1435747884&type=full"**[/IMG2]

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                      • #12
                        Re: Outboard only starts after manual priming of cylinders

                        Yep using manual choke fully on

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                        • #13
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                          Re: Outboard only starts after manual priming of cylinders

                          Originally posted by briaineo View Post
                          Yep using manual choke fully on
                          I had a similar problem but on a Yamaha,being a tech it drove me crazy.had to use carb ceaner to start and run great till it sat after shutting off.finally by accident I found out one bat was sulfated[ seemed to crank ok but low volts on cranking ].probably not ur prob but just wanted to let u know.good luck

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