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Hi all,

I have a problem with my Rotax 912 UL. About 16 years old and maybe 600 hrs.
It started during flight at full power. Total loss of power. Throttle back to idle and the engine kept running. Slowly reapplied power and the engine ran just fine...
Until the next start. Loss of power after about 40-50 seconds. Throttle back and returned to the field. Could apply two shots of power and reached the field. Fixed the plane on the ground and applied full throttle. Seemed to be OK.
Next start same story. Loss of power after about 40-50 seconds. Throttle back and returned to the field.
So I started checking all I could think of.
Ignition circuit one and two (normal drop of rpm)
Fuel outlet in the tank. (Found some debris, not the cause)
Fuel cock. (Found some debris, not the cause)
Electric fuel pump and gascolator (made a bypass, not the cause)
Mechanical fuel pump (got a new one, not the cause)
Replaced all hoses
checked the carbs (no debris)
checked electronic modules according to TB 912-06
checked ground connection according to TB 912-02
checked the spark plugs (looked fine)
checkt the force to rotate the engine without sparkplugs.
(looked fine, less than 50nm)
checked the muffler (no noise when shaking, all openings open)
checked a bottle of whiskey (no more ideas)

I would appreciate it if anyone had any ideas
Thank you for reading!
  • Re: Total loss of power

    by » 12 years ago


    Hi Hans,

    Two things come to mind. You still have an intermittent electrical connection, but I think I would pull the carbs off, dis-assemble them and clean them out with carb cleaning spray and blow them out with air pressure. You could easily still have a carb issue here and it isn't visible with just removing the bowls. Things hide. Sometimes the shortest time for a solution is the longest path. Pull the carbs and clean them or spend many more hours trying to find the problem. I would do the carbs first, this sounds more fuel related until proven different. Then go after the electrical side.

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


    Thank you said by: Hans Meier

  • Re: Total loss of power

    by » 12 years ago


    Hi Hans

    Im with Roger on this. There is a possibility that there could be a sliver of rubber or something on the fuel pipe side of the fuel inlet into the carb. This would need blowing out from inside by removing the needle valve.

    It could also be the floats starting to degrade and pieces intermittently blocking the main jets, as well as lots of other intermittent blockages.

    I wouldn't hesitate in removing and completely stripping, cleaning and blowing out everything with an air line, and rebuilding with new o-rings.

    I would also replace all the fuel pipe between the filter and the cabs incase it is starting to perish if you haven't changed it all.

    Good luck

    Mark

    Thank you said by: Hans Meier

  • Re: Total loss of power

    by » 12 years ago


    The idea that two carbs would both have a power loss synchronously and at an even repetitive interval is a little challenging for me. Sounds electrical to me. I'll be interested in what is determined.

    Thank you said by: Hans Meier

  • Re: Total loss of power

    by » 12 years ago


    Hi James

    A fuel blockage in one carb would cause a dramatic loss in power as the engine could not run on two cylinders.

    If the fuel flow to the carbs was below the fuel required for full power due to an inlet blockage, then as the engine is running on full power the fuel level will be dropping in 1 carb. After 40-50 seconds that carb has no more fuel to support fuel power and so you will get a dramatic power loss.

    I am not say both carbs are getting blocked at the same time and then clearing at the same time.

    Mark

    Thank you said by: Hans Meier

  • Re: Total loss of power

    by » 12 years ago


    I'm with Mark.


    You may find debris in each carb bowl, but typically it is only one carb that gets blocked off at that specific time and power goes right into the trash. I usually see it down from full throttle to 3800'ish.

    Here is a fast "self rescue" you can do in the field with just a screwdriver to check and unblock a carb debris issue. I have used it a few times and it works well. At least this way you won't be stranded and need to call for help unless it is something other than carb bowl debris.
    Remember to make a safe landing first.

    This video was made on a specific plane and your setup right around the carb may differ, but the basic principle should work for anyone.

    http://www.youtube.com/watch?feature=player_embedded&v=JdS7OtbcxwY

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


    Thank you said by: Hans Meier

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