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Thread: ROTAX 912UL - Loss of Power Issue

  1. #1
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    ROTAX 912UL - Loss of Power Issue

    Team

    I need your help with a 912UL

    On Tuesday, went flying, all was good, the flight was uneventful, landed, had a brew, and off I went again.

    This time just after take-off, the engine lost power, rev counter dropped to about 4300rmp from 5000rmp, cut the throttle and landed, engine still ticking over taxied to the end of the strip where I carried out a full engine run, no problems there, did a high speed run down the runway, no problems, so turned around and gave it another try… same thing happened, loss of power on take-off.

    Taxied back to the hangar, checked the fuel, in fact I put new stuff in. Checked the fuel filter and carb bowls for debris… nothing found.
    Put new plugs in it…

    Started the engine, even had the lads tilt her skyward so simulate take off angle of attack… no problems found.

    Taxied off and, began the take-off phase… this time now engine power loss. Flew for about half hour, landed. Had a cuppa, then about an hour later, carried out the pre-flight checks as I fancied another quick flight before heading off home, this time whist in the clime out, another power loss, this time not enough runway to land, so I did a wide turn and landed back on the runway, put the her away in the hangar …a little confused.

    Today, I stripped down the carbs, cleaned them out, found a few Orings that looked suspect so have ordered two rebuild kits.

    However, I really don’t think that would cause the engine to lose power…

    So guys, what do you think, anybody got any ideas what to do next

    Looking forward to your replies
    GT

  2. #2

    ROTAX 912UL - Loss of Power Issue

    Hi Gary, I had a similar issue with the 912 in my Skyranger. I did all the obvious checks and changes, and nothing stopped this issue of rough running on climb out.
    I then 'cleaned out' the fuel return pipe and restrictor jet, and it stopped the problem, as I think I was getting vapour lock when the engine was getting hot.
    Brian.

  3. #3
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    ROTAX 912UL - Loss of Power Issue

    Hi Brian

    Thanks for your reply, i will check these out on monday, will have a full day... driving me round the bend lol

    GT

  4. #4

    ROTAX 912UL - Loss of Power Issue

    Hi Gary,
    Give it about 5 or 10 seconds with your electric pump to "push out" the vapour lock. Is the fuel stale, try dumping the fuel and putting in fresh fuel. Vapour lock sounds the most likely issue, winter grade fuel is more likely to vapour lock.

    Return pipe and restrictor jet is a good suggestion.

    When you solve the problem please let us all know.

    Nick.

  5. #5
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    ROTAX 912UL - Loss of Power Issue

    Hi Nick, Will do, and thanks for your suggestion

    GT

  6. #6

    ROTAX 912UL - Loss of Power Issue

    i'd suspect fuel pressure. how old is the fuel pump?

    colin

  7. #7
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    ROTAX 912UL - Loss of Power Issue

    Hi Colin

    the pump is about two years old, with about 40hrs running time on it

  8. #8

    ROTAX 912UL - Loss of Power Issue

    I would think vapour lock is unlikely - I don't have the return on our Nynja and never had on my competition Skyrangers and flew them in Spanish desert heat of 40C plus. And no electric pump either.

    It sounds like a fuel restriction is most likely. We had similar with an Aircreation trike that would do it once in a blue moon then started to get more common. Turned out to be a sliver of rubber fuel hose in the carb inlet which when the mood took it would float over and block the flow. With one carb starved of fuel it lost a lot of RPM and ran rough. It was only found with a good carb strip and back blowing with compressed air.

    You havent got any of that dodgy batch of semperit fuel tubing have you..? Or one if the dodgy AC fuel pumps?

    the other thing that can cause this is if you have lengthened the carb overflow vents - if extended to vent out the bottom of the cowling then when flying they are in a much lower pressure area than the carb intakes and it leans the mixture and engine loses power. A few folk have made this mistake. I had a similar thing with a mixture control which ended up with carb static vents in the cockpit. Big pressure difference in flight and engine virtually stopped at 300'. Took all day of problem hunting until we figured it out..

    Paul

  9. #9
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    ROTAX 912UL - Loss of Power Issue

    Hi Paul,

    The Skyranger has not suffered any problem until the other day. its not that it runs rough, it just seems to lose power.

    It has a new type fuel pump, which Gaza Masters installed, and I do have a return vapour tube on the system, as per the build manual.

    I will check out and give the carb a good blowing out

    Cheers Paul

    GT

  10. #10
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    ROTAX 912UL - Loss of Power Issue

    Throw fuel filter away Gary and start from there,even if replaced not long ago it may have something blocking as Paul said it does seem like something is being drawn in place restricting fuel flow,I would use compressor pls back to tank and see if anything appears in tank,clean inlet valves into carb etc,good luck,it will always be in the back of you're mind even when cured

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