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50hp Yamaha

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  • 50hp Yamaha

    This ones got me!!! 1989 50hp yamaha 2 stroke.Just got this thing on a project boat.History was owned by old guy from new and has 200hrs on it.
    Got it home,compression tested it! all cylinders 130psi.
    Next i pulled the head!! No corrosion at all so on went a new head gasket,new plugs etc.
    Next i changed impeller,gear oil! all good,pumps good water.
    Stripped and cleaned carbs,new float needles,gasket etc etc
    Pulled all the wiring off and checked connections for corrosion and made sure all the earths were good.
    Ignition coils are good! Stator looks like new!!
    Heres the thing!! In idle it will run for exactly 30 seconds and then just die.
    She will start straight back up every time and die after 30 seconds!!
    Anything over idle and she will run all day.
    Checked the fuel pump and the diaphram has no splits and looks good.Also put a clear hose on after the pump and didnt have any air leaks going to the fuel rail.
    Could the CDI be faulty at idle??? Its the one with the metal timing dial on the front of the CDI unit.
    Any advice would be highly appreciated because this one has got me stumped!!!
    Also if the idle timing was off would that cause it to run for exactly 30 second then die?

  • #2
    Are you dead sure the carbs needle valves and seats are working freely?....30 seconds sounds like the time to drain carbs float chamber before it starves for fuel....


    • #3
      Use a timing light to see what the timing is doing during statrt up.
      I believe during start up timing is increased causing motor to idle a little high, then drops back to what the specs call for .
      usually idles high until motor warms up(temp switch tells the CDI it is warm), and them it just has a short timer that lets it increase for some time.
      my C40TLRX idle spec is 7 ATDC not sure what your 50 is.

      make sure you follow the link and sync procedure every time you put the carbs back on.
      carbs may not be synced properly or the idle jets/ passages are not completely clean or not set set properly.

      does this motor have a choke or is it a prime start motor?
      that old of a motor may not be even close to my 1999, so not sure if the timing is controlled by the CDI electronicly or if it have linkage to move a timing plate under the flywheel
      Last edited by 99yam40; September 21st, 2017, 07:30 AM.


      • #4
        Yeah carbs are clean and are full when this happens.Removed drain bolts and fuel comes out.
        It has quickstart so will idle higher for 10 or so seconds then goes back to normal idle speed.Its after thats,say 20 seconds later it will just die.Has a slight shudder then dies.I will check idle timing today.
        I have also tried a completely different tank and primer bulb with same results.
        I put a timing light on it when it does the stall and the light fluctuates when its cutting out but to me that sound normal as the flywheel starts slowing down before the stall.
        Could it be as simple as a weak fuel pump at idle??? The fuel system holds pressure and the primer bulb stays hard.Although i have tried manually pumping the bulb at idle when it cuts out with no affect.


        • #5
          Yeah its got electric choke! Switch on the control box


          • #6
            if the motor has electric and manual choke it does not have the prime start system


            • #7
              Its got an electric enricher on the bottom carb and an electric choke which closes the carb plates


              • #8
                Abit of an update!! checked the part number on the cdi box and it wasnt the correct box for my year.I just borrowed a cdi of my friend that has the same outboard and now the thing wont idle without the fast idle lever all the way up and is spewing out unburnt oil and fuel out the prop.
                Put my timing light on each cylind and am getting spark.
                MMMM really doing my head in


                • #9
                  Well just stripped the carbs again and noticed alot of crap in the bowls.Must be getting through the stock yammy inline filter.Soaking carbs again because i sprayed carb cleaner through the idle passages and it seemed that they had a restriction somewhere.
                  That may have been the problem the whole time.Just strange that it would idle for exactly 30 seconds and die.
                  Will update in the morning when i reinstall them


                  • #10
                    Anyone have any idea??
                    Just soaked,cleaned and blew out carbs again.Different CDI box,different working stator.
                    Brand new fuel pump and lines,definitly no air getting into system.
                    Does the same thing!
                    Will idle for 30 seconds then die like you have turned the ignition key off.
                    It will start straight back up and idle perfect again for 30 seconds and die.
                    Anything over idle it will run all day???


                    • #11
                      Another update!!! Pulled the linkage that connects the timing dial on the CDI and advanced it 3/8 inch advanced and guess what??? She stays running!!!
                      Shes running abit rough so just got to set the timing in the piss when i get a chance.My timing light showed she was set at about 3 degress when linked up to the timing indication marks on the CDI.
                      Anyone else had there CDI box not timed correct when you do the link and sink as per manual and the dial is lined up with the timing marks on the box??


                      • #12
                        yes, I had to replace my CDI to get the idle timing correct on my C40TLRX when the marks lined up following the link and sync procedure in the service manual.

                        what are the timing specs on your motor?
                        did you monitor the timing when 1st started like I told you to see how it changes after warm up?
                        Last edited by 99yam40; September 24th, 2017, 04:12 AM.


                        • #13
                          No i didnt check the timing like you said only verified it was getting spark.Idle timing on this motor is 7+-1 atdc and looks like when you do the link it idles at 3 degrees or abit lower.
                          I disconnecting the linkage and moved the timing dial by hand until it idled at around 6 degrees and it didnt snuff out and was idling around 850rpm on the muffs.
                          I then adjusted the connecting arm to match that new position and when you give it a little bit of throttle the timing advances with the carbs and sounds perfect.
                          I have to check wot timing and see if i will still get the correct degree for that.
                          If i do i cant see why it wouldnt work???


                          • #14
                            Well another update!!!!
                            Tried timing the outboard properly and the timing light was very dim!!! Meaning i could only just see the timing indicator on the flywheel!!!
                            The timing light is 10 years old so i was thinking its just old!!
                            I took my light to my brothers 50hp yamaha and it was super bright!!!!
                            I then put the light on my lawn mower hahahaha and it was also super bright!!!
                            So it seems i have weak spark at idle????
                            Any ideas?? I dont have a working dva adapter atm.
                            Could all my problems be as simple as my low speed coil in my stator not working properly???
                            Meaning it runs for 30 seconds and builds up heat and cuts spark???


                            • #15
                              Sign up today
                              time to get a DVA and measure charge coil output and all CDI inputs & outputs to find out if they are a problem

                              My C40 does not have but one charge coil, have no idea if your has more than one