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Yamaha 50hp idle problem

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  • Yamaha 50hp idle problem

    I have a 1997 50tlrv motor. The only problem it still has is on cold starts it lets out a high pitch squeal and dies. I linked a video of what is happening(motor had been sitting for one week). If I start it semi cold, as in sitting over an hour it lets out one squeal but never dies. After that initial high pitch squeal it idles great and runs great at any rpm and jumps the boat right on plane. It has only even let one squeal per start. And does not do this if started warm. Any ideas what this is?
    Last edited by Skeeter00185; 3 weeks ago.

  • #2
    that is what is called a lean sneeze.
    fire backs up into the crankcase burning the incoming fuel/air charge.
    it is not good on the seals and reeds

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    • #3
      How do I fix it?

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      • #4
        clean the carbs and prime start enrichment system to make sure they all work as they should during cold starts

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        • #5
          This system is new to me. The prime start system is that red switch on carb #2 right? Is it supposed to be flipped up to open or down for closed? It was flipped up and the motor would only idles on one cylinder cause it was flooding the other two, so I flipped it down and it idles great after that squeal.

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          • #6
            Okay, think I found my problem, I can’t run the motor to be sure, but I was able to find a video on the prime start system, and found that that red switch has three positions. Normal, closed and emergency. I was running on emergency when it was running on one cylander. I had it on closed and am assuming that was restricting fuel flow and creating the lean sneeze. I got it to normal now so we will see what that does.

            one more question, how many turns out should the needle be on the carbs?
            thanks for your help

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            • #7
              Okay, finally got a chance to run the motor. It starred easy and did not do that squeal, however now the engine is misfiring at idle. Is it possibly getting to much fuel now with the switch turned to normal instead of off?

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              • #8
                yes it is possible if the heater unit is not heating up and shutting off the extra fuel as the motor warms up

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                • #9
                  So I must have just had good luck the first time, but now it’s back to acting the same way. Squeal and dies.
                  Before I pull the prime start assembly and look at it, I wanted to ask, is there anything simple I could be missing? Like do you have to push the key in to engage it like you would a choke? I have not been doing that.

                  If I pull this to clean it out, what all needs to be replaced? I assume the diaphragm and seals, anything else?

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                  • #10
                    stuff hiding in the lines and pump can block off jets and passages in the carbs if you do not clean it all after cleaning the carbs

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                    • #11
                      That should not be the issue, I replaced the fuel hoses and pump. Basically did the whole fuel system, except for the prime start. I’m gonna try pulling it apart and cleaning it.

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                      • #12
                        Update, I took apart the prime start system and cleaned it up good. Nothing seemed wrong, the diaphragm was in good shape, but replaced anyway. The gasket was really worn and was not sealing good, so I think air was leaking in and causing the fuel mixture to be less rich causing the lean sneeze. It no longer lean sneezes on a cold start.

                        I have one other question on this though, is it possible to turn the fast idle down? It runs at 3k rpm on the hose when cold started, then slows down to 800rpm. 3k seems way to high to me.

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                        • #13
                          check to see what the timing is doing during that cold start up.
                          timing is the only way I can think of that the CDI can adjust Idle RPM
                          Last edited by 99yam40; 1 week ago.

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                          • #14
                            Okay, I’ll have to research how to do that, but just curious, is 3k normal for a cold start? I know it’s higher cause it’s on the hose, but what should it be?

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                            • #15
                              do you have Yamaha gauges on this motor/boat to read RPM, or you guessing at 3K?
                              how long does it run at 3K, before it drops back to normal.
                              I never paid too much attention to what RPM it starts at, I will have to look next time I fire up my C40.

                              a Timing light is used on an outboard just like on gas automotive motors
                              Last edited by 99yam40; 1 week ago.

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