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2003 Yamaha 40hp 4 stroke bogging

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  • 2003 Yamaha 40hp 4 stroke bogging

    Have a new to me 2003 yamaha 40 4 stroke.
    I boat the engine yesterday and ran it for the first time today. It was winterized prior to the sale.

    It runs great at a low idle and can get up rpms under no load. When in the water, when I throttle it up it bogs down and cuts out. If I nudge it up slowly, eventually I can get it up on a plan and run like heck. If I power down and try to power up quickly, it bogs down or completely stalls out.

    Any thoughts?

    Bob

  • #2
    Re: 2003 Yamaha 40hp 4 stroke bogging

    sounds like its time to clean the carbs paying speacial attention to the acceleration enrichment circuits.
    you should also check for fuel restrictions with a vacum guage and a T fitting installed just in front of the fuel pump intake, vacum should be less than 4" Hg and at least about 1/2" Hg at or near WPT.
    no tech questions by PM, they wont get answered.
    you have to be trusted by the people that you lie to .

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    • #3
      Re: 2003 Yamaha 40hp 4 stroke bogging

      make WPT a WOT
      no tech questions by PM, they wont get answered.
      you have to be trusted by the people that you lie to .

      Comment


      • #4
        Re: 2003 Yamaha 40hp 4 stroke bogging

        Thanks for the tips. What is "WPT" ?

        Comment


        • #5
          Re: 2003 Yamaha 40hp 4 stroke bogging

          wpt was a typo.
          but if I try to use the edit function my poor machine all but shuts down so I dont normally.
          why didnt ya read the second reply ?
          no tech questions by PM, they wont get answered.
          you have to be trusted by the people that you lie to .

          Comment


          • #6
            Re: 2003 Yamaha 40hp 4 stroke bogging

            Now I get it. Thank you.
            The engine is an 04, not and 03. The carbs were just cleaned, new fuel filter and a fuel/water separator added. When I recieved the boat, the tanks were dry. I started with fresh fuel, also filling the separator prior to hooking up the fuel lines.

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            • #7
              Re: 2003 Yamaha 40hp 4 stroke bogging

              test spark, test compression, then go chase fuel.
              I dont care if the carbs were brand new this morning,if they got trash in them this afternoon Guess what ?
              its Suck,Squeeze,Bang and Blow. been that way for over 100 years.
              when a gasoline engine,especially a 4 stroke, has a rapid opening of the throttle you MUST add extra fuel or a POP or total stall will result regardless of anyother issues.
              as you stated with a gradual throttle opening it runs well I dont suspect compression or spark issues but they should be tested.
              the chemically correct burn mix of gasoline is about 14/1 air to fuel. at about 16 to 1 the mix becomes to rich to ignite, at about 13to 1 it becomes to lean to burn. as its a constant volume fuel you must add or subtract fuel with the throttle opening.
              diesel is a constant combustion type fuel and does not require air throttling and will burn in a 300-1 range from high to low.
              gas is about a 3-1 range.
              so based on your description when you open the throttle rapidly either there is not enough fuel in the fuel bowls for extra enrichment or the acceleration circuits are defective/dirty.
              no tech questions by PM, they wont get answered.
              you have to be trusted by the people that you lie to .

              Comment


              • #8
                Rebuilding Carb ( was: Re: 2003 Yamaha 40hp 4 stroke bogging

                I'm considering rebuilding the triple decker carbs. I have rebuilt lots of carbs on lawnmowers, chainsaws and chevy engines, so I am hoping that I am not getting involved in something that I shouldn't. Any suggestions before I start. Can I get a carb kit from this site.
                Thanks Bob

                Comment


                • #9
                  Re: 2004 Yamaha 40hp 4 stroke bogging

                  Have implemented all suggestions.
                  Spark check out
                  compression checks out
                  Fuel pump pressure is good
                  Carb rebuilt
                  Changed all filters, 6 gal tank, checked little titty on fuel line (and it is nice and firm when squeezed) - just like the old days.

                  How about timing? I have a light, but not the know how.

                  Or, is it time I bite the bullet and bring it in?

                  Thanks again,
                  Bob



                  The motor still dies out when doing a "hole-shot" (really fast acceleration).

                  The only thing I have not done is timing. I have a timing light, but

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                  • #10
                    long shot since post is so old but rpelton I would really like to know what the problem ended up being. I have exact same problem.

                    Comment


                    • #11
                      Sign up today
                      Originally posted by Oxygen View Post
                      long shot since post is so old but rpelton I would really like to know what the problem ended up being. I have exact same problem.
                      Long shot is right. He hasn't been here in 12 years.

                      Closed.
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