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Hot start problem

in 912 / 914 Technical Questions 9 years ago

  • Re: Hot start problem

    by » 9 years ago

    OK, here's some additional info, don't know whether it'll jiggle some thoughts or not. As a reminder, I'm having a problem hot starting in my RV-12 after letting the hot engine sit for 10 - 15 minutes. Pilot side EGT runs up normally but passenger side EGT is basically dead for 60 seconds or so after which the engine smoothes out and runs fine. Starts fine if I immediately restart after shut down and starts fine if I let it sit 30 - 45 minutes.

    I didn't notice this before but, after I shut down after one of these difficult starts, I found a wet spot that smelled of gasoline on the concrete under the exhaust pipe. That would seem to indicate flooding, not starvation like I'd expect of a vapor lock that I'd been assuming was the problem.

    I've tried various throttle settings from 1/8" to nearly full throttle. Full throttle seemed to work best but still not great.

    I tried shutting off the fuel valve to starve the engine at shut down rather than just turning off the Ignition switches as someone suggested earlier. That didn't correct the problem but did cut down the time to when the right side started running from 60+ seconds to about 10 - 15 seconds.

    The choke on both sides does go to full close when the choke lever is pushed in.

    Any thoughts? I really don't want to restart after a short shutdown any more - it's just too hard on the engine, mount, etc.
      
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  • Re: Hot start problem

    by » 9 years ago

    It's possible since you are dumping fuel that you need to set the carb float height and or you have a leaking needle valve that needs replacement (or has debris in it). Since the RV12 guys had quite a few of the bad floats I would take the time to weigh them.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: Hot start problem

    by » 9 years ago

    That's a good thought, Roger, I'll do that. I have the new floats but did have one of those go bad.

    Would that, or a needle valve problem, manifest itself this way (starts and runs great except if I try a hot start after a short wait)?
      
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  • Re: Hot start problem

    by » 9 years ago

    If the remaining pressure in the fuel line floods the carb then yes it would be hard to start and you could have fuel venting that you are seeing. You can have pressure in the fuel line for a while because as the fuel heats up it expands or even vaporizes a bit and builds pressure.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: Hot start problem

    by » 9 years ago

    I looked through the post, I did not see any mention of a fuel return line. Does your rv have a fuel return line?

    I have noticed that with the fuel return line the fuel pressure drops to zero within a second after shutdown. Without a return line the fuel pressure remains at 5-6 psi at shutdown, for how long I don't know, but if you have a carb fuel valve seating problem this could lead to a flooding situation .
      
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