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2017 Yamaha F20 Cold starts and stalling at idle

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  • 2017 Yamaha F20 Cold starts and stalling at idle

    Good Afternoon All,

    I've got a newer Yamaha F 20 tiller model that runs great for the most part, and is very dependable. My issue with it is that after running it for a while and warming it up, if you goose the throttle a bit then drop back to idle, it will almost always stall out. I also have a bugger of a time getting it to run right when its cold out. Maine cold that is. Used it this morning at 39F and 38F water temp. It will run for a moment, but then before it warms up, it leans back out and stalls. Then its a hard job getting it running again. If you can get it into gear without it stalling, it will finally warm up properly and start up well for the rest of the day.

    Its a ultra low emission engine, so I suspect its leaned out to within an inch of its life, and I cant figure a way to adjust it. Can I have a shop adjust that mix so it'll run better in the cold and when dropping back to idle, or is it set from factory never to be messed with again.


  • #2
    I would separate the issue of hard-to-start-when-cold from the issue of it stalling when you rev up and come down (after it has warmed up).

    On the carburetor, you can adjust the pilot screw and the stop screw. But the enrichment system is Prime Start, and you can't adjust it.

    If you goose the throttle when it's still cold, does it stall out less often? If so, I would say your Prime Start is working, but you're just too lean normally. If you take it to a shop, I would just ask them to clean, rebuild & adjust the carburetor.

    Sometimes you can clear up a partial clog in the carburetor jet by fast-idling it and holding a rag over the intake for a few seconds. And sometimes a fuel treatment like SeaFoam can help (but not usually).
    2011 F50TLR, 2010 G3 V167C


    • #3
      Can you please post the exact model of your engine from the data plate.

      I would suggest that your carburetor is in need of cleaning. Is this engine new to you or have you had it since new? If you have had since new, has this always been a problem?

      I operate a friends F15 with the same carb setup as yours and it starts no problem in much lower temperatures then have starts and warms up fine. When the prime start circuit was plugged a few years ago it was very difficult to start and warm up.


      • #4
        To add, have you checked the thermostat to make sure it's functioning properly?

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


        • #5
          Thanks for the responses all, I was away for a bit so I couldn't answer right away.

          I agree, the cold starting issue is a separate issue. It starts great in the summertime, but in the cold it doesn't seem like the "choke" stays engaged long enough to warm the engine so it will lean out and stall. Then when you try to restart it, (pull start of course), it doesn't seem like the "choke" will re-engage at all, so it doesn't catch well and doesnt like to stay running. If you can get it into gear without it stalling and drive around for a few minutes, it warms up nicely and then will restart very well until it gets cold again. I havent checked the thermostat for functionality, but since it does eventually warm up properly, I don't suspect that is the issue.

          The motor tag has says 6AHK, and F20SMHA and S and 1055963 and Z. And the manufacture says 04/15, not 17. My mistake.

          The bigger issue is the stalling. It does it just as much when cold as when warm. The agency I work for has had the motor since new, but I took over operation and maintenance of it in september of 2018. It has been to a shop since we have owned it, it has always had the stalling out when quickly dropped to idle issue. If you can gently ramp down the throttle to idle, it wont stall, and it actually idles and runs very nicely. I use it to set fish nets, so there is a lot of forward backward operation and quick bursts of throttle to position the boat properly. I have used seafoam in it to try to clean it out, but there was no effect. I also set the idle higher, which caused snapping when put into gear, and didn't fix the problem. The shop it went to was not a professional dealership type shop. Is that the next step? Bring it to them and have the "mix" adjusted? Thanks