Full throttle goes to Idle

Discussion in 'Boat Design' started by Txbaseball, Jun 14, 2014.

  1. Txbaseball
    Joined: Jun 2014
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    Txbaseball New Member

    I have a 1988 sprint bass boat with a 110 Johnson. The boat runs great up until I go gull throttle. This is my first boat and I was wondering what it could be. Without going full throttle I have gotten it up to 37mph. However, once I go full throttle it instantly goes to idle. I'm not sure if 37 is all it will go or if there is an actual problem. I was just wondering if anyone knew what it could be, thanks.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Defeats me. What rpm gives you 37mph ?
     
  3. Txbaseball
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    Txbaseball New Member

    I believe it was running between 2,500 and 3,200 rpms. I am going to take it out tomorrow and hopefully will be able to give a better description of what is happening.
     
  4. messabout
    Joined: Jan 2006
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    messabout Senior Member

    Examine your throttle linkages. It sounds like a full throttle setting is causing the throttle plate to close. You may be able to do an easy fix for this problem. The engine is surely capable and willing to turn 5000 or more.

    If the engine is an EFI type there will be throttle position sensors. That'll be an electronic do-dad that communicates with the engine control module. The problem could be a bit more complicated if there is something wrong with one of the electronic feedback components. There will be several of them, including a mass air sensor and maybe even an O2 sensor. None of this is mind bending technology but appropriate test equipment may be necessary to diagnose the problem.

    Check the throttle linkages for the first round of inspections.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    I agree the throttle linkages need to be checked, I can't imagine how it would be returning to the idle setting, though, as the throttle is opened. But, take the cowl off and see what happens as the throttle is fully opened (motor not running) as regards carb butterfly opening etc. This motor would not be EFI,imo.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Agreed, it's likely something simple, but could be a few different, some subtle issues at play. The first part you should buy for your boat is an engine manual.

    [​IMG]
     
  7. Grey Ghost
    Joined: Aug 2012
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    Grey Ghost Senior Member

    Long shot... clogged fuel filters and water filters caused weird things to happen to me before.
     
  8. PAR
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    PAR Yacht Designer/Builder

    Filters usually act up regardless of throttle settings.
     
  9. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    Breather on the fuel tank cap? Enough to stop a 25 or 40 from full chat at 5k rpm.....
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    It is a case of losing revs sharply, not just not getting maximum revs, so I'd doubt that could be involved.
     

  11. SukiSolo
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    SukiSolo Senior Member

    Maybe, but funny things happen if you get a partial vacuum from the fuel tank. It is also worth checking that the breather actually breathes, I have known the internal passageway of the breather cap to become clogged too.

    If it is a carb engine (and not fuel supply/breather problem), I'd be cleaning out the floatbowls, passageways and jets because by half throttle the engine is running on main jet and needle pretty much exclusively.
     
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