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Fuel venting/dripping out air filter/intakes 912S

in General Tech Discussion 10 years ago

  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    I personally did not feel comfortable mixing the threads because the fuel fitting looks so weak with not much meat. Important discussion on this but sure would like some help on the over pressure I am getting and the problem I am trying to solve:

    Again after installing the fuel pressure gage and testing:
    Fuel pressures were interesting. Engine not running and boost pump on about 1 1/2 PSI. Ground run about 5 PSI idle and 2 PSI full throttle. Looks normal and within range. But flight had a range of 6 1/2 PSI at idle was the highest I saw. Climbed to 11,000 MSL and saw about 1 1/2 PSA at full power, yikes.... Boost pump brought it up to 3.

    So the 6 1/2 at idle is far above the 5.8 Max PSI for older fuel pump but below the 7.26 for the new fuel pump serial number 12.2059 which I have. They are the same carbs but one fuel pump allows greater pressure than the older. So if I had an old fuel pump I would be above the max which the rotax operators manual said will override the float valve and vent fuel as I am doing but I am below the pressure allowed for the new fuel pump. I am thinking that I need to increase the oriface size of the return line to lower this 6 1/2 PSI which is probably venting the fuel. Thoughts on this fuel pressure?
      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    I think you need to go back to the float valves:
    The Heavy Maintenance Manual test (attached) says they should hold 5.8PSI with just the weight of the float arm and the valve holding it closed.
    Did you try this test?
    How bad are the carbs shaking at idle?
    Do you have room to fit an airbox?
    Floatvalvetest.pdf (You do not have access to download this file.)
      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    Installed pressure regulator to get max 3.75 psi and same problem, fuel out the air filters, not what i expected. Yes next is to pull the carbs and do the test as well as check the float level in the process. Hard to coordinate my rotax mechanic and take my money machine out of service. If it fails this test what is the fix? At this point i will do anything.

    Yes we balanced the carbs first to get it running smooth first off. No room for air box.
      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    I would look closely at the float valve seat. It should really hold around 10-15 psi without any leaking. A little bit of corrosion or debris in the seat can prevent the viton tip needle from getting a tight seal. Might be some debris in there to clean out. otherwise, if it's corroded beyond repair, Bing sells a replacement seat... But Rotax doesn't authorize the replacement, so if you're an SLSA you legally can't replace it. But if you're an ELSA you can... It is an experiment after all!
      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    Just an FYI, I had the same issue with the carbs on my 912ULS. I purchased the mityvac as Roger and Rob suggested and did the test and found my brand new float needle would not seat. I was able to get them to seat by polishing the seat with some fine valve lapping compound. I used and old needle and glued the end to a small wood dowel so I could spin the needle and valve compound on the seat. I did this a few times to each seat, tested them again and now they hold 10+ psi without leak down. Installed them back on the plane and no more leaks.

    Brent Hoskins
    Caldwell, ID
    Thank you said by: hal colliver
      
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