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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

    Rob,
    I spent all day yesterday finding a m1 1 which goes to a 5/16 darb, not the optimum. So you are saying a 1/8 NPT thread will go into a metric m10 1 thread. I am a never heard and a little concerned mixing english and metric threads. :unsure:
      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    Yes, Rotax has chosen this thread as it fits 1/8NPT (the most common size for sensors)
    They also have the same thread on the oil pump for the sensor. Even the new oil pump with the M10 sensor can be fitted with 1/8NPT.
    Another example is the magnetic plug fits both a 16mm or 5/8" wrench.
      
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  • Re: Fuel venting/dripping out air filter/intakes 912S

    by » 10 years ago

    OK. Me being the extra cautious person with my new 912S I will test it with a metric m10 1 nut and 1/8 pipe thread.

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

    by » 10 years ago

    I tried the 1/8 inch pipe thread in a m10 1 nut and the fuel line pressure port and could only get 3 threads so I decided to go with my m10 1 metric thread to 5/16 barb to install a pressure gage.
    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. :unsure:

    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

    Paul

    You CANNOT mix a 1/8 NPT thread with a M10x1. They are completely different threads and you will damage something.

    1/8 NPT is an imperial TAPERED thread with 28 TPI

    M10x 1 is a metric PARALLEL thread with 25.4 TPI

    They are worlds apart but you could force them together if you tried, but you will damage one or both fittings and they could come apart under pressure.

    Using the wrong size spanner is not the best practice either, but you won't do as much damage.

    Mark
      
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