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White spark plugs

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  • White spark plugs

    The spark plugs are too white on both my o7 DF 150 engines, I had maby 100 hours on the plugs before changing them, 300 hours on each engine. I changed the IAC valves on both maby 15 hours ago. How can you richen up the mixture? Do they have oxygen sensors like a car? I don't run the boat very much ,idle them on muffs every 3 or 4 weeks to keep them running. Afraid of burning a piston. Any ideas ? Thanks
    Engines run fine, no alarms.

  • #2
    No you cant change the mixture, its all done by the ecu. The early engines like yours dont have O2 sensors.

    First, make sure that the correct spec spark plugs are being used.

    More than likely, given what you said, the problem is stale fuel. Stale fuel loses its octane and can cause pinging and related issues. Bad.

    The solution is to always add stabiliser to the fuel to keep it fresh every time you fill up. And, a tank that is kept full will stay fresh longer than one that is not full. In hot humid conditions, fuel goes stale quicker than in cold dry climates.

    But where you are now is with a tank full of probably stale fuel.

    Ideally you could drain it and start over with fresh fuel, and treat it with stabiliser as mentioned. I like Fuel Doctor. But any auto or marine shop will have some kind available. Or, if the tank is half full now, fill it with the highest octane fuel availabe.

    If you cant do that, you can try adding octane booster to try to restore it, then use as much as possible from the tank as quickly as possible. Then add stabiliser to match the amount of new fuel added.


    • #3
      Dont think its the fuel, always used non ethanol premium with treatment . Runs fine.
      Just found in the manual that you need to plug it into a computer with the Suzuki software and install a temporary O2 sensor while letting it self tune at several RPM ranges.


      • #4
        Premium unleaded actually loses octane rating faster than standard unleaded. Given the usage profile you described, stale fuel remains the most likely issue. If indeed there is an actual issue at all.

        I have never heard of anyone needing to retune as you’ve described.


        • #5
          Suzuki manual says to check the O2 feedback system every two years or after extended usage to see if worn or old parts may have changed the fuel air ratio.
          . I will run it on new gas and recheck. You probably right , the motors should not need it with only with a little less than 300 hours on them.
          Thanks for the info.