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Engine bogs down -- comments appreciated

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  • Engine bogs down -- comments appreciated

    2001 OX66 on a 25" walk-around . . .motor starts, idles, runs great. . .just tuned, plugs, caps, cleaned O2 sensor, VST tank, fuel filter, water separator, etc. . . .while speeding along at 5500-5700 rpm, the engine just starts to slow down . . .no missing, coughing, etc . . .just like starving for fuel . . .BUT when I touch the trim button up or down, the engine picks back up and runs strong again . . .when I put it in neutral and rev the engine, it goes up in rpm quickly and smoothly. . .my local Yamaha dealer speculated that there may be bad electrical connections at the battery causing momentary lack of electricity, and when I touch the trim the surge of electricity corrects the motor.

    I replaced the batteries last summer . . they are charged and I get 14.4volts while running.. .checked the connections and all seem OK. Your thoughts?

  • #2
    That’s a good clue. Electrical “power loss” somewhere. I would clean all grounds first. The ones bolted to block.


    • #3
      I agree, bad connection somewhere .
      also reving a motor in neutral does not do anything except possibly harm it,
      proves nothing without a load on it


      • #4
        How far of an RPM drop and how old is the O2 Sensor?


        • #5
          When you "checked" the battery connections, did you remove the cables?

          Did you clean the terminals and cable ends with a brush as well as check for any corrosion inside the end of the cables?

          Lastly, do you have an on /off main battery switch installed?
          1997 Angler 204, Center Console powered by a 2006 Yamaha F150


          • #6

            If you don't touch the trim switch, how far do the rpms drop?

            Also, is this a 200hp?
            Last edited by rejesterd; 6 days ago.
            2011 F50TLR, 2010 G3 V167C


            • #7
              Whaler9113: RPM drops to about 3000 and seems to go lower before I trim it up or down; don't know age of O2 sensor but it was very clean when I took it out for cleaning --- TownsendsFJR1300: Yes, removed cables, but I did not remove cowl and check motor connections yet, will do today once the rain stops. Yes, I have a new A-B switch. ---Rejestered: it is s 250 Saltwater Series


              • #8
                Does it slowly drop to 3000? Or does it immediately drop to 3000 then slowly get lower after that? The reason I ask is because there might be multiple issues going on, where the engine puts itself into a control mode and you have an electrical connection issue on top of that.
                2011 F50TLR, 2010 G3 V167C


                • #9
                  rejesterd: it slowly drops to 3000 . . .but I know what you are meaning by going into control ode . . .doesn't seem to do that. Thought initially it may be a filter problem in the VST, but I haven't run it much since deep cleaning and thorough maintenance last summer . . .not much use since the hurricane Michael in October. It does not seem to be missing, coughing, sputtering, etc. It just drops RPM and then goes like heck again when I touch the trim button and move the motor up or down a bit.


                  • #10
                    Agreed.. if it was the VST filter clogging up, it probably wouldn't just drop smoothly like that.

                    I think you ruled out a bad battery or rectifier/regulator, because you're seeing 14.4V when running. So I would do as someone suggested previously and check all the grounds on the engine itself.
                    2011 F50TLR, 2010 G3 V167C