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Troubleshoot fuel F20

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  • #1

    Troubleshoot fuel F20

    OK, so I'll throw this out there for any advice:

    Yamaha F20 BMH 2013 on small fiberglass fishingboat, used 90% for slow *****ing on idle. Idles perfectly smooth for hours on end. About ~130h this summer. Runs and revs awesomely on WOT (since you helped me with new prop) Has never misfired or "coughed". Starts on "2nd" pull, which I attribute to "it needs to pull up the fuel". Cold starts 100% on 2nd pull, restart on warm engine can be both 1st pull and 3rd pull due to I need the throttle set rather high to restart. All in all I've suspected fuel to be the reason for 2 pulls when cold and sometimes a 3rd when warm.

    Now the recent issue: when on idle, *****ing, it has suddenly died out on me. Like a 2-3 second event with lowering rpms and cut off, just as if I would run the carb dry. Restart becomes nearly impossible It doesn't even splutter when I use starting fluid. I pull and pull but it seems almost as dead as if no spark, no signs of life. I've reprimed bulb, I can see gas in filter, opened tank to reassure no vaccuum. The stall gives virtually no warning. And after I've pulled what seems like a 100 pulls, it starts. I give it some gas and run WOT for a while. Then it can run for hours on end in idle again.

    My uneducated guesses are: carb float and needle gets stuck during prolonged idle or fuelpump malfuction on low revs for prolonged time?

    Next time it happens I was thinking of unscrewing carb drain to see if bowl is empty, but other than that I don't know how to diagnose?

    Any help is as always welcome, sorry for a rather long question.
    //Merc200, sweden
    Tags: None
  • #2
    If it doesn't even "splutter" with starting fluid, then it seems like it's not a fuel problem wouldn't you think??

    Comment

    • #3
      Originally posted by ausnoelm View Post
      If it doesn't even "splutter" with starting fluid, then it seems like it's not a fuel problem wouldn't you think??
      Yea, I know, that part is surely strange, but this far I can't rule out the starting fluid has gone bad/old.
      I have such a hard time figuring out why ignition should be the issue when it has never ran unevenly.
      I even checked the lanyard (dead mans grip), since we once found water inside it, but it was dry.

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      • #4
        test for spark when it will not start to rule that out.

        Not sure if starting fluid would help fire if too much fuel is already in the cylinder.
        something to think about

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        • #5
          I would check all your wiring and connections as well, especially the kill switch wire in the tiller handle. Seems to me you are losing spark.

          As noted already check for spark next time it happens. Do you have a small spark tester that you can carry with you?

          Comment

          • #6
            Engines dislike prolonged idling; the incomplete combustion at low revs with excess hydrocarbons in the exhaust is the reason vehicle idling is discouraged and stop start technology was introduced. I suspect plugs are sooting up so pulling one next time it stops would inform. A frequent blast at WOT might help but for prolonged *****ing a small electric outboard is a better solution.

            Comment

            • #7
              Originally posted by 99yam40 View Post
              test for spark when it will not start to rule that out.

              Not sure if starting fluid would help fire if too much fuel is already in the cylinder.
              something to think about
              I've had the same thought, as if the excess fuel can quench starting fluid.

              Originally posted by panasonic View Post
              I would check all your wiring and connections as well, especially the kill switch wire in the tiller handle. Seems to me you are losing spark.

              As noted already check for spark next time it happens. Do you have a small spark tester that you can carry with you?
              Wiring and spark is in need of a check, but a dilemma is that it eventually starts without me touching any wiring. A small spark tester, is that one that you use without removing the plugs? A penlike thing that touches the sparkplug hat? If so I can get one very cheap to carry onboard.

              Originally posted by cleddau1 View Post
              Engines dislike prolonged idling; the incomplete combustion at low revs with excess hydrocarbons in the exhaust is the reason vehicle idling is discouraged and stop start technology was introduced. I suspect plugs are sooting up so pulling one next time it stops would inform. A frequent blast at WOT might help but for prolonged *****ing a small electric outboard is a better solution.
              Yes, the first time it happened, I removed the plugs when I got home. They were very sooted up (despite the engine had started up again and ran the rest of the fishing trip) Sooted up enough for me to react on it, because I've kept an eye on the plugs twice a year in recent years. And my 4-stroke engine spark plugs have always been reasonably clean and dry, more to the "brown" rather than the black sooting.
              I cleaned them and lightly brushed them with 400-grit.
              Yes, autumn fishing here is almost exclusively *****ing, since northern pike runs deeper, they're hard to find with casting.

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              • #8
                Something like this.
                Attached Files

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                • #9
                  Originally posted by panasonic View Post
                  Something like this.
                  Yes. But with the sooting I prefer the old fashioned way to see the actual spark.
                  But yes, I will keep an eye on spark!

                  Comment

                  • #10
                    When you are out on the water and this happens again...trying to check spark the old fashion way may cost a plug and wrench lost overboard...and maybe yourself. The one shown is put in place between the cap and plug and is hands free, which I think you will need haul the engine over...just saying.

                    Comment

                    • #11
                      Originally posted by panasonic View Post
                      When you are out on the water and this happens again...trying to check spark the old fashion way may cost a plug and wrench lost overboard...and maybe yourself. The one shown is put in place between the cap and plug and is hands free, which I think you will need haul the engine over...just saying.
                      Throwing tools and fishing apparel overboard happens, and I love to avoid it. Myself wouldn't happen, sober since the early 2000's =)

                      But that tester, does it show wether spark actually sparks or just that ignition gives it power? (Not very much electrician, but I doubt any fault in the ignition, ignition would mean abrubt stall, and or small stalls or misfires)

                      But perhaps the tester is dependant on wether the plug actually sparks?

                      But I get it is tool free to plug in the tester between plug and ignition cap.

                      BTW the sparkplug I new since late spring, has about 130 hours on it.

                      Comment

                      • #12
                        Originally posted by 99yam40 View Post
                        test for spark when it will not start to rule that out.

                        Not sure if starting fluid would help fire if too much fuel is already in the cylinder.
                        something to think about
                        The spark is insanely small, tested in the backyard, almost not visible in daylight. But the sound was easier to hear. And I suspect that sparks aren't greater than that nowadays. I will describe what I found in my carb below:

                        Originally posted by panasonic View Post
                        I would check all your wiring and connections as well, especially the kill switch wire in the tiller handle. Seems to me you are losing spark.

                        As noted already check for spark next time it happens. Do you have a small spark tester that you can carry with you?
                        Since the issue happens again, and this time I found that the carb bowl was empty, I opened the carb. And from what I can tell this far, the screw that clamps down the float (over the horizontal "pivot"-pin) had come undone. I remember I was insecure about that screw when I cleaned the carb, since clamping it finger tight felt as it gave the float to little movement, so I loosened it as much as I dared so that the float moved freely and further up and down. It must've been this, now the screw was way out. Somehow the float was able to get stuck this way.

                        And the issue of restarting on starting fluid is most likely the carb "butterfly-valve" is closed unless I open the throttle, which I didn't. silly me.

                        I have not tested the motor, but something tells me this was it, since it had all the signs of running out of fuel. Lost its revs in 2-3 seconds on idle and stalled.

                        Comment

                        • #13
                          You should be able to tighten the screw good and snug, that holds the float pivot pin in place. If not... there is something wrong with the pin or the float itself.

                          Tightening that screw down should not cause the float to stick.

                          Perhaps the pin is bent slightly.

                          Comment

                          • #14
                            Originally posted by panasonic View Post
                            You should be able to tighten the screw good and snug, that holds the float pivot pin in place. If not... there is something wrong with the pin or the float itself.

                            Tightening that screw down should not cause the float to stick.

                            Perhaps the pin is bent slightly.
                            OK, that is very good to know, actually. Because I felt as if I tightened it "snug", as in a firm twist with the screwdriver without overdoing it, it clamps down too hard on one side of the pivot pin and makes the other side of the pin lift up from its seat. But if it is supposed to be snug, then I can live with that the float doesn't need more movement.

                            It was the very obvious difference in float movement that made me set it a little loose. But I think you are right, the float only needs very few millimeters of movement to open and shut the needle.

                            I will open it again and set it. Thank you

                            Comment

                            • #15
                              never saw one lift the pin when tightened.
                              may want to be sure it is sitting in the groove properly.
                              float should swivel on the pin/ shaft freely

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