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Have a RV-12 with a Rotax 912ULS. In February 2014 it ran like a charm. Then, in preparation for the DAR inspection and Airworthiness Certificate, I took out the fuel tank and opened up the aircraft for inspection. But, I needed the Aircraft Registration first. Took over ten months to get the correct registration (ELSA) out of the Ok City FAA Registration Branch. The Airworthiness Certificate took only seven days. Then I put the aircraft back together.

Engine, which has less than an hour on it, will try to start and run ten to twenty seconds, then die. RPM gets up to about 1200. Acts like it is starving for fuel. The electric pump is good, the fuel shutoff valve is good. I cleaned the screen (didn’t find much) of the gascolator. Fuel flow out of the gascolator is good

Pulled four spark plugs. They appear good and are dry.

The Bing carburetors’ bowls have fuel in them. I did not empty the carburetor of fuel (100LL) during the year the engine was sitting waiting for FAA paperwork. Did find some debris in the float bowls – kind of white pieces of sand. Putting the white sand pieces between my fingers and rubbing, the sand turned to a white paste. Cleaned out the bowls. The floats in both carburetors ‘float’. The main jet easily moves up and down. The idle jet appears clean (I have not removed it). Sprayed carb cleaner on the main and idler jets and then blew canned air on them.

Tried to start the engine again today and got the same result. With the throttle full back to idle and the choke full on, the engine will start, but then dies after a ten to twenty second run. With the choke off, the engine will not start.

Any suggestions on what I should try next?
  • Re: 912 ULS, 100HP, Will Not Start

    by » 9 years ago


    Sure sounds like fuel starvation. Is your fuel tank cap vent free and clear? Alternatively, is your fuel tank venting system free and clear? Did your fuel system successfully pass the fuel flow test as indicated in the plans? Is your fuel pressure showing at least a couple PSI with the electric fuel pump activated?

    Thinking out of the box here but,... could it be running for some 10-20 seconds on the initial SoftStart timing and then not advancing to the regular timing due to an electrical glitch or incorrect hook-up??? Unlikely if you had no problems on the earlier run.

  • Re: 912 ULS, 100HP, Will Not Start

    by » 9 years ago


    Chuck, What happens if you push the choke back in, right after it starts, and add throttle?

  • Re: 912 ULS, 100HP, Will Not Start

    by » 9 years ago


    Found a bunch of gunk at the fuel inlet to the carburetor. Kind of a white pasty gunk. Cleaned out the inlet on both carbs. Engine started. Runs rough over 2,000 rpm. Jets in carbs are clean and clear. Will pull spark plugs, check them, and do a compression check.

  • Re: 912 ULS, 100HP, Will Not Start

    by » 9 years ago


    Hi Chuck,

    If you found that much "white pasty gunk" in the fuel line at the carb and it still runs rough then those carbs need to come off and be cleaned. Strip them, use carb cleaning spray in every orifice and follow that by air. You can chase this issue for a long time, but my guess it will need to be done. If it were me I would just get it done and be done with it. It really won't take that long and is easy to do. While the carbs are off check the float armature height.

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


  • Re: 912 ULS, 100HP, Will Not Start

    by » 9 years ago


    You need to find the out what this gunk is and where it came from before flying again. Let us know what you find.

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