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Yamaha 50DETO PrimeStart not working correctly

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  • Yamaha 50DETO PrimeStart not working correctly

    Hi all

    Need help with the 1989 yamaha 50DETO. Seems that the prime start or automatic/choke is pretty much allways on roughly 15-20seconds and running high rpm regardles wether the engine is warm or cold.
    When the prime start goes off the enging is idling at the normal rpm and you can put the gear on.
    Prime start can be turned off using the lever but that does not solve the issue itself. Any ideas for this issue?

  • #2
    sounds normal to me.
    timing is advanced for start up/warm up and drops back to normal idle timing

    put a timing light on it and see what it is doing


    • #3
      At operating temp, (a decent run) and you turn it off and then on again, do you still have that 15-20 second high idle?

      If the engines up to full temp, that idle shouldn't be high as the engines NOT WARMING up, it's already at temp.

      I don't see your engine in the US parts section, can I assume your outside the US?

      Last edited by TownsendsFJR1300; 1 week ago.
      1997 Angler 204, Center Console powered by a 2006 Yamaha F150TXR


      • #4
        Thanks for the replys. Yes it was like that high idling 15-20secs after every startup even after warmed up. im outside of US (FIN), so those engines vary, but not much.
        But anyways i ended up to find the reason, but cant explain it right away. The fuel pump was malfunctioning some how. There was no visible damages on gasgets or diabraghms but changed those while the pump was allready disassembled. After replacement the engine was working way much better. Still high idling after cold or warm startup but the rpms was like 2000rpms 15sec which is ok as i can put the gear on. Before the replacement the rpms was like 4000 15sec.


        • #5
          well 4000RPM at start up is too high.
          my C4TLRX starts and idles at around 1200 for the warm up and then drops down to 800
          even 2000 is too high to be putting into gear, you will end up damaging something

          do you have a tach to measure that RPM or are you just guessing?
          A link and sync of the carbs includes checking to make sure the timing is also correct.

          does that old of a motor still have the timing plate tied to the carb linkage?
          you might want to check to make sure it is not sticking and holding the timing too far advanced
          Last edited by 99yam40; 1 week ago.


          • #6
            Plus 1, ^^, it's still high.

            As asked above, what is the actual idle RPM now once settled down??

            Almost sounds like an air leak running super lean...

            1997 Angler 204, Center Console powered by a 2006 Yamaha F150TXR


            • #7
              He must be guessing at the RPM.


              • #8
                Hi and thanks for the advice.
                Yes i got the rpm readings from the tach. Now it seems to work pretty well. Cold start radings are around 1500rpms and after a while around 1000rpm. Have to say that the original reason was not even the fuel pump but the fuel hose between the filter and the pump. It was not an original and was a bit too long replacment. So it bended too much preventing the normal fuel flow and thats why the prime start was acting weirdly.
                Last edited by pasikoivi; 4 days ago.


                • #9
                  Might want to adjust the idle down a bit, (7-800) as it's hard on the LU, shifting..

                  Glad you found the issue
                  1997 Angler 204, Center Console powered by a 2006 Yamaha F150TXR


                  • #10
                    I'd never even think of putting my motor in gear at 40000 RPM!..... Or even 2000....them poor clutch dogs!....