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Yamaha 50 power loss issue

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  • Yamaha 50 power loss issue

    I have a 1997 50tlrv, it idles and starts great. It usually runs 6000+rpm but today I took it out and. Will not go over 5000 no matter what trim I’m at it does not top 5000.
    The main issue is that it won’t even go to 5000 sometimes. It will go to 4000-4200 at full throttle, then randomly, without moving the throttle it all of a sudden jumps to 5000.
    almost as if it were down a cylinder and then it kicks on.
    anybody have any ideas where to start? Does this sound like timing, compression, spark, fuel, etc.
    i appreciate any input

  • #2
    always good to check compression, spark, and timing to start out with when problems show up, just be sure those are good
    fuel pump would be my next thing to check
    too much fuel to air or too little is not good for a cylinder to burn properly
    Oh yea, 6000+ is not good for a motor that Top RPM is suppose to be 5500


    • #3
      It has a Brand new fuel pump


      • #4
        that does not let you forget the other things I posted


        • #5
          I won’t, just wanted to ad that to it.
          I appreciate the feedback. I will check into the other possibilities as time allows and let you know what I find


          • #6
            Okay, motor has good compression and fuel is not the issue. It acts exactly like a spark problem because it’s like somebody flipped a switch and it runs great then will cut back.
            my plan is to pull plugs to make sure they are not fouled, clean coil grounds and bullet connector connections, and see if that doesn’t work if I can isolate which cylinder.
            many other simple things anybody could recommend checking before I get into anything further such as coils and cdi?


            • #7
              timing light will show what the timing is doing and also if spark is getting to the plugs, just have to move the light to the different plug wires to make sure one or more is not getting spark when problem shows up


              • #8
                Okay, so I took plugs out and plugged them in and watched for spark, cylinder one had no spark, so I swapped the 1 and two coil. Now cylinder two had no spark but cylinder one did.
                I could not find a new coil in stock, but I’d do find an old used one of a Yamaha two stroke. It wasn’t exactly identical but the mech sic said it will work just the same. Went and ran the boat and it ran so much better but every now and then it would do the thing where when you hammer down it takes a cylinder 10-20 seconds to kick in. Which was a huge improvement over before because it is doing it way less frequently and it doesn’t take as long to kick in.

                should my next plan of action be to get a new oem coil and see if that fixes it 100% or do you think there is something else that would be causing my issue? Again, it got so much better with this used coil but not perfect yet


                • #9
                  why not test the coils to see if they show in spec or not?
                  also I would be testing the peak voltage inputs and outputs of the ECU to make sure they are in spec.
                  need to know if all parts of ignition system are meeting spec.
                  and then you might have a wiring problem

                  Finding a intermittent spark problem can be tricky

                  I need to ask how you decided fuel in not a problem?
                  too much or too little fuel to air in a cylinder will keep it from burning properly
                  Last edited by 99yam40; 3 weeks ago.


                  • #10
                    Okay so to report back
                    the motor misfires bad when cold started but after warning up has no issues idling other than if I trim it up high it starts misfiring again.
                    the coils are in spec so that is not the issue.
                    I just pulled the carbs off and cleaned them and found no issue, the fuel pump is good to.
                    When running it will top out at 5100 at 27mph when it usually runs 5900-6k at 35.
                    I checked compression from top to bottom it is 117,117,112

                    my only other thought, could I have a reed valve issue? At idle I hear a very faint chirping from that area. Other than checking that what recommendations do you have? I was reading in my manual and it says I need a cdi tester which I do not have so I cannot check the cdi at the moment.


                    • #11
                      DVA adapter and regular meter will give you peak voltage readings
                      you really need to know if the inputs and out puts of the CDI are meeting minimum peak voltage specs

                      As I said before an inductive timing light hooked to the individual plug wires should show if spark is not happening when you say you have a miss fire

                      also chirping to me could be a lean sneeze