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914UL power fluctuates drastically when in turbo

in 912 / 914 Technical Questions 10 years ago

  • Re: 914UL power fluctuates drastically when in turbo

    by » 9 years ago

    i have just spent a huge amount of time trying to solve the problem with surging on my 914 engine. The revs would not go above 4200 rpm and drop off to 2500 then surge again . I went thru everything including having the waste gate and complete turbo removed and inspected by specialist. It is not the turbo or the waste gate. My engine has only 260 hrs.I also changed the fuel regulator suspecting it may be the problem.
    My problems started suddenly when i installed the carb overhaul kit supplied by Rotax .
    Part of the kit are 2 o rings that are intended to be installed under the bolt that holds the carb bowls on. At the time of installation I thought it stange that a bolt head would keep a o ring tight, but there was nothing else in the kit .
    The result is that the carb bowls are not tightened sufficiently and suck air somewhere.
    I replaced the o rings with the fibre washers that was originally installed below each bolt.
    Bingo and the engine went straight up to over 6000 rpm static with prop on .
    The carb kit does not come with anything other than the 2 o rings.
    I think it is really poor of Rotax to supply the kit with the wrong parts.
    Good luck.
      
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  • Re: 914UL power fluctuates drastically when in turbo

    by » 9 years ago

    I had a case of surging on a 914 which to this day I am unsure why it occurred. Problem came on gradually getting worse and worse over a number of flying hours. I was called in when the problem got so bad they couldn't continue flying it.

    Engine would surge from 3000Rpm to 5500RPM. The amount of surging would worsen the more the throttle was opened. It was as if the throttle was being opened and closed in about a 3 second cycle.
    We tried all sorts of thing including locking the wastegate, removing the turbo pipe. They all seemed to improve it, but not cure it.
    Eventually we discovered the springs in the carbs were catching on the inside of the pistons causing the pistons to lift irregularly. New springs fitted and the problem disappeared. To this day I cant explain it, but it may be worth a try.
      
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  • Re: 914UL power fluctuates drastically when in turbo

    by » 9 years ago

    This problem is still not solved.

    We are checking the carb bowls for tightness and leaks. it appears not to be an issue.

    I noticed that it is also pulsing at lower power settings. Above 30 inches it becomes a problem.

    I have lubed the waste gate and checked the cable it all looks good.
    I have noticed the TCU making some noise prior to starting the engine.

    I used a computer and the tlr program to monitor the engine on the ground. I did not detect a problem but am not sure what to look for.
      
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  • Re: 914UL power fluctuates drastically when in turbo

    by » 9 years ago

    Are you sure the wastegate is adjusted properly?
    With the throttle at idle turn the master ON.
    The wastegate should open (spring relaxed), and then close again (spring extended)
    At this point the wastegate arm should be pulled firmly tight by the servo.
      
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  • Re: 914UL power fluctuates drastically when in turbo

    by » one year ago

    You should check if the carburetor bowls are not deformed, the manual indicates that the Attachment screw should be tightened to 49 inch/pounds but that torque is enough to deform the bowl and cause problems when the turbo kicks in.

     

      
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