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2004 115 two stroke

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  • 2004 115 two stroke

    I have a very well maintained 2004 Yamaha 115 two stroke. During the last three outings when I attempt to run over 4400rpm's, it seems as if the computer tells the engine to drop rpm's. I have to slow to idle, take it out of gear, then it will get back on it. If I stay below 4400rpm's it runs fine. Any ideas?

  • #2


    • #3
      model # please.

      Are you getting any alarms going off?

      Is the engine run in salt water and is so, flushed with fresh water after every use??

      Is the water pump fairly newish, t-stats?
      1997 Angler 204 CC, 2006 F150 TXR


      • #4
        Yam 115

        If it may help, I had a similar problem on a 130.
        Turned out to be the battery 'kill switch' I had installed in the boat.
        It was rusted inside and reduced the voltage to the motor causing the rev limiter to kick in.
        Low voltage can cause the symptoms you are describing.
        Try cleaning your battery connections on both the motor and the battery.
        There is no task too simple for some people to complicate!
        Challenger 16ft - 1999 Yamaha 130 BETO


        • #5
          I have been changing the water impeller, fuel filter(s), spark plugs, and the lower unit oil every two years. I also re-pack the trailer bearings at the same time. I am due in January to perform the maintenance. I haven't added an hour gauge yet but I will add it this go around.

          No alarms has sounded.

          I have not changed the thermostat but will add it to the list.

          I will check the battery and electrical connections and run some voltage checks tonight and post my findings.

          I'm fairly certain that the computer is shutting down the motor. I have to bring it to idle and shift to neutral and it will pick right back up. I don't even have to kill the engine.

          I was thinking that it may have an issue with the two-stroke oil system not keeping up...

          I appreciate y'all's willingness to help!


          • #6
            Test the alarm system to make sure it works.
            Do you have gauges that will indicate overheat or low oil?
            If not you will have to check oil level when it happens.
            if oil level is the problem there is a inline filter that can restrict flow

            Still no model #
            Last edited by 99yam40; 11-04-2014, 01:04 PM.


            • #7
              Model number 115TLRC

              I have never ran the oil low enough for the sensor to alarm. I wasn't aware of any filters in the oil system. It only makes sense that it would have one. I will check and clean it tonight.


              • #8
                You need to be methodical in your trouble shooting, you are "suspecting" everything possible, without proper testing, and can rule out nothing, buy a manual for your motor and follow the steps outlined, no guessing.....


                • #9
                  Originally posted by firftrZ71 View Post
                  Model number 115TLRC

                  I have never ran the oil low enough for the sensor to alarm. I wasn't aware of any filters in the oil system. It only makes sense that it would have one. I will check and clean it tonight.
                  Have you tested the alarm yet?
                  So do you have gauges?
                  Do they indicate anything when RPM reduction happens?
                  No need to take things apart until you get an idea of what is happening
                  Last edited by 99yam40; 11-04-2014, 06:24 PM.


                  • #10
                    I haven't had a chance to check the audible alarms yet. I went into the shop where I normally keep it and forgot that I've had another project parked in my boat's "bedroom". As far as the gauges, the only one that may help is the RPM gauge. It reads correctly 90% of the time. Sometimes it reads higher RPMs but as far as I can tell, it hasn't had any adverse effects while the motor is running. It seemed to be working correctly when I've had issues.

                    I do run the boat in saltwater from time to time, but I flush it with a water hose first then earmuffs.

                    Since I live just north of SA and the rain this evening is coming down in buckets and the weather forecast calls for heavy rains and floods for the next three days, it doesn't look like I'll be able to test anything anytime soon. Maybe the service manual will come in between now and then...

                    Please keep checking this thread. I'll post the answers to your questions asap.


                    • #11
                      My guess is you live above San Antonio here in Texas from what the weather looks like on radar.

                      I believe that motor should sound the buzzer if you pull the lanyard off the kill switch and turn the motor over with the key switch.

                      to test overheat you can ground the pink wire going to the overheat switch on head.

                      Drain oil tank then turn on key switch to bring in low oil alarm and watch it fill,
                      make sure the remote tank as plenty of oil.
                      Always good to drain the water trap on the motor tank from time to time to make sure it stays good and clean oil being injected into motor
                      Last edited by 99yam40; 11-05-2014, 08:17 AM.