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no maximum power 912 ul

in 912 / 914 Technical Questions 14 years ago
We have a dynamic wt9 with a 912ul. Al of a sudden we could not get maximum power anymore. We only get around 4600rpm. We checked the fuel lines, airfilter boxes, plugs and one carburator. A strange thing is when we measure the vacuum it loses vacuum when we ref up. Has anyone sugestions?

with kind regards
Freerk Bouwer

  • Re: no maximum power 912 ul

    by » 14 years ago

    You most likely have an obstruction. It could be in a carb and it could be in the line. Most likely a carb. Put a set of vacuum gauges on and the one that is running the most vacuum is usually the culprit. If you have dirt in one you may have some dirt in the other and it just hasn't shown up yet. I would clean both well and you should be on your way. You will need to pull this carb or both and remove the jets and blow out all jets and holes in the carb body. Do it right the first time and you won't have to pull them again. While your at it you may want to blow out the fuel lines from the gascolator up to and out the carb supply lines.

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

    Thank you said by: Freerk Bouwer
      
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  • Re: no maximum power 912 ul

    by » 14 years ago

    We have had the vacuum meters connected and they show equal settings. so the syngronisation is ok. But the thing is that the meters show less vacuum when we increase the throttle. With no vacuum at all showing at maximum throttle setting. We cleaned already the fuel lines and one carb with no debris at all. The decrease in the vacuum is strange we think because when testing on another aircraft the vacuum is increasing when we increase the power setting.

    So we are very much puzzled.

    Freerk Bouwer
      
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  • Re: no maximum power 912 ul

    by » 14 years ago

    The vacuum is supposed to go down as you apply throttle. The more air and fuel it receives the less it is sucking for vacuum. Just take the throttle to 3800-4000 and look and see if one carb has a big vacuum difference. If they are in sync at this mid range throttle setting then your problem is on the high rpm area and that means you have a fuel flow issue either in the lines (you said you blew these out) or in the fuel flow through the carb with a passage way, the float needle or the float adjustment which controls how much fuel is in the bowl. If it doesn't then you need to pull both carbs completely and flush and blow them out. If you don't completely strip and blow each passage in the carb out then you may be chasing your tail and have to do it again. I am taking for granted you checked the gascolator and fuel filter already. Like I said in the previous post, if you don't do a good job the first time you may need to pull them and do it again. Better to do it only once. I say this from learning the hard way and from many years experience.

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

      
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  • Re: no maximum power 912 ul

    by » 14 years ago

    Thanks for our quick reply. We have changed the fuel filters from both tanks. We will cleanout both carbs and then try again. We do not suspect the needles because at midrange power there is not much difference in the vacuum gauges. The power loss also appeared all of a sudden, with no difference in the engine setup. It happend in midair :( .

    We will be back on this issue.

    Thanks again Roger

    Freerk Bouwer
      
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  • Re: no maximum power 912 ul

    by » 14 years ago

    Once the carbs are pneumatically synchronized, obstructions in the carb jets or fuel supply will not affect manifold pressure. It will remain essentially the same even though one carb may be delivering much less fuel to the fuel air mix.

    Bill.
      
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