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Bloody new fuel pump

in 912 / 914 Technical Questions 13 years ago

  • Re: Bloody new fuel pump

    by » 13 years ago

    Jay,

    One thing I forgot. If you are vibrating below 2000RPM and the carbs are balanced, check the idle screws. They should be turned out 1 1/2 turns if I remember correctly. Also make sure both enrichener circuits are closing all the way after startup.

    Bill.
      
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  • Re: Bloody new fuel pump

    by » 13 years ago

    Many of the older planes did not get a recirculating line, but all of us should make sure one is installed.

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

      
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  • Re: Bloody new fuel pump

    by » 13 years ago

    make sure you have a recirculating line. This is how this pump was designed. It is a must have and if you don't it wll most likely over pressure.


    I did some tests by putting a ball valve in the return line. The difference in fuel pressure with the line closed verses open was a 0.3 psi drop when the return line was open.
    If 4.4psi is the normal range of operation and the new pumps were designed around the fuel return line being installed, the pump should give 4.7psi max.
    Dave
      
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  • Re: Bloody new fuel pump

    by » 13 years ago

    Hi Dave,

    Facts just learned over the last 9 days in Rotax school.
    High pressures usually occur at idle because you aren't using much fuel compared to cruise fuel usage. The return line issue with these new pumps was confirmed during the Rotax class I just came back from. All the new pumps without hose already installed are being tested in the Bahamas before they come into the US. It was confirmed with Rotax that these new pumps have to have a re-circulation line. Average pressure was 4.5 psi and yes just a few failed, built a very small number. What they did find is a huge number of gauges tend to be wrong and not the pump. When and electric pump was added into the mix the pressure went up another .5-1.0 psi. Many of the high pressure readings in the field have not been from the pump, but gauges and sending units being off anywhere from .5-2 psi. This is why it is important to double check your actual reading with a calibrated mechanical pump at idle.

    I'm just relaying what was learned in the Rotax classes. They made a special calibrated test stand in the Bahamas to check the pumps. The difference bertween them and us is they actually used a gauge that was calibrated and right on the mark.

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

      
    Report

  • Re: Bloody new fuel pump

    by » 13 years ago

    Accepted. All I am saying is that the return line with the 0.35mm orifice does not give any significant pressure drop. I measured the pressure drop with two different mechanical gauges. They were not calibrated, but were the standard Rotax mechanical pressure gauges. I still believe the new pumps should be giving out no more than 4.7psi. If this is what they do, then we don't have a problem. If Rotax say in their manual that an aux pump should not exceed 4.4psi (to prevent over-pressurising the carbs) the same should apply to the mechanical pump.
    Dave
      
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