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Nautica Rib Mercury Sportjet idles perfectly, bogs over 3K rpm; one plug dry, clean

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  • Nautica Rib Mercury Sportjet idles perfectly, bogs over 3K rpm; one plug dry, clean

    Hello,

    I have a 90 HP Mercury SportJet in my Nautica Rib that won't go over 3K rpm without bogging or stalling. I pulled the plugs and the top two look normal (light oil/gas mix, not dripping or fouled) and the bottom plug looks brand new and dry, like it's fresh out of the box. The plugs are new NGK B9HS-10's.

    The boat is setup to run on premix (40:1) and has one carb feeding all three jugs. It runs beautifully below 3K rpm -- fires right up, idles smoothly. It just won't kick into high gear.

    I plan to change the plug wires (as soon as I can find some) and change the fuel filter. I thought I'd also try squeezing the primer bulb while it's running to rule out the fuel pump.

    Here are my questions:

    1. If the #3 plug is dry and looks new, is it starving for fuel (and therefore lubricant) and if so, is it at risk for a piston meltdown? If so, I won't try anything else until a mechanic looks at it.

    2. Could it instead indicate a lack of spark in #3? I noticed that there seem to be issues with triggers/stators on these.


    Any assistance you could provide would be great. Thanks!

  • #2
    Re: Nautica Rib Mercury Sportjet idles perfectly, bogs over 3K rpm; one plug dry, cle

    One Carb ???? Not on a 90 hp Sport Jet , Is this a conversion ???
    ANOMALY
    1994 Bayliner Reflexx
    90 hp Merc / Force Sport Jet

    If you do not like my advice, Remember , My Boat Runs , So can yours
    If you are not ready to spend $25 for a manual for your boat then sell it
    He Man Outboard Haters Sport Jet Club .... president

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    • #3
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      Re: Nautica Rib Mercury Sportjet idles perfectly, bogs over 3K rpm; one plug dry, cle

      Originally posted by kend301 View Post
      One Carb ???? Not on a 90 hp Sport Jet , Is this a conversion ???
      It seems to have been converted, and the carb seems to work fine. It's also converteid to premix. Is there a way to check for spark in the bottom cylinder?

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