75hp mercury bogs down at full throttle

Discussion in 'Diesel Engines' started by majorpepper, Mar 22, 2015.

  1. majorpepper
    Joined: Mar 2015
    Posts: 3
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    Location: lake placid florida

    majorpepper New Member

    My 75hp mercury bogs down at full throttle. I took it to a marine shop and they emptied the fuel tank because it supposedly had water. Replaced fuel line an pick up tube. Cleaned carburetors and fuel line. They lake tested and said it was fine. I took it out and still bogs down at full throttle. I discovered the priming bulb was not staying full. I took it back to the same shop and explained the problems again. This time they found water in the carburetors and debris in fuel pump they replaced the fuel pump diaphragm. They lake tested it and claimed it was fine. I took it out and is still doing the identical thing, I a tired of throwing money away. Looking for help.
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Maybe you have water in the boat's fuel tank. Do you have a water trap on the fuel line ?
     
  3. majorpepper
    Joined: Mar 2015
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    Location: lake placid florida

    majorpepper New Member

    Yes I have a fuel/water separator.
     
  4. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Could be air entering the fuel system. What you could do is take a friend on the next test run, and have them keep pumping the primer bulb while you drive the boat. By the time they get a cramp in their hand, you should know whether it is fuel starvation or not !
     
  5. majorpepper
    Joined: Mar 2015
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    Location: lake placid florida

    majorpepper New Member

    I have done that and in fact as long as they keep pumping the boat runs fine. I am just wondering why the shop can not find the problem. I have explained every issue to them in detail..
     
  6. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,386
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    Location: Australia

    Mr Efficiency Senior Member

    The engine manual trouble-shooting section may offer a clue that you have overlooked. But at least you seem to have isolated the problem to fuel delivery. It is possible a needle valve is sticking, or there is a faulty fitting along the fuel line admitting air. Try another workshop, if possible.
     

  7. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Welcome to the forum.

    Fuel bulbs and the hose to and from it will break down with ethanol fuels, so they need to be replaced from time to time. Why don't you just start with a level playing field and replace the hoses, bulb, any filters, etc., clean the full length of the system (again) and start over, knowing what's good and what isn't.

    The first part you buy for this engine is the manual. It's the best 30 bucks you'll toss at it. Once you've got it working, you can run through the diagnostic section and get a really good assessment of the rest of the systems and the necessary routine maintenance associated with this engine.
     
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