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I experienced engine roughness on climb-out (this will absolutely get your attention!) with a drop iin Fuel flow pressure in the 2 range. (2014 SportCruiser 912ULS). Been uising 100% 93 mogas with ethanol. Now been told to use a blend of 30% 100LL with the mogas. Also learned, from another source, that there is a winter and a summer blend of mogas which may affect the boiling point.

This was the second flight of the day. Surface temp was 32 cent at 50 AGL. Fuel pressure came back up to normal range after leaving 2500' to 1400' and 2-4 minutes.

Once on the ground, opened the gascolater. Small stream. Turned on Fuel pump and the stream may have decreaded in size but certainly did not increase.

Been told by several that there may be a design problem with the cowling not allowing sufficient cool air to pass by the engine.

Any advice?
  • Re: VAPOR LOCK

    by » 8 years ago


    I have seen this a lot and even in my own plane. After I fly somewhere for breakfast and come out about 45 min. later the fuel pressure will be low. I usually just run the engine for a couple of minutes at a higher rpm than idle (i.e. 2500). This usually takes care of the hotter fuel in the lines and helps bring in cooler fuel from the re-circulation line and fuel going through the pump. I haven't heard of anyone near me having any rough engine because of the lower pressure. I have 3 Sport Cruisers that come to see me and known have this problem, even with 91 oct ethanol fuel. If I remember right the fire sleeve on the Sport Cruiser fuel line is pretty thin and the metal fuel line fittings on top are fully exposed. You could try replacing some of the fire sleeve with the thicker more insulated fire sleeve and make sure those metal fittings have fire sleeve around them. try running the engine a tad longer on the ground at a higher rpm to bring the cooler fuel in.

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


    Thank you said by: Don Kaltenbach

  • Re: VAPOR LOCK

    by » 8 years ago


    Don,
    I had a 2010 PiperSport that I put 800 hours on. On one occasion, where the outside temp was 105, on climb out I had a momentary power loss for about a second. Landed and found no other problem. I had waited in line about 15 minutes and did a normal run up. I use only 91 or 93 ethanol free 95% of the time.

    I now have a 2014 Sport Cruiser. I believe the summer blend is much less likely to have vapor lock. I generally leave the electric fuel pump on until about 2500 AGL. I think Roger is spot on about running at a higher RPM for a couple of minutes prior to take off if the second or more flight of the day, or like my situation where it is very hot and having to idle for quite a while.

    Thank you said by: Don Kaltenbach

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