Posted for Wayne Marshall <waynefmarshall@comcast.net>:

  Dan: I have 52 hours on my Legacy now and just went through nearly two
months of high fuel pressure problems when retarding the throttle at altitude.
After consulting many documents and talking with many professionals on the
subject, here's what solved the situation. First it is normal to get an
initial climb in fuel pressure when retarding the throttle at altitude with
the prop set up in a normal cruise position (24 MAP) and the mixture fairly
rich. You will notice that the pressure is controllable by retarding the
mixture a bit or bringing the prop down too. What finally cured it was
removing all fittings that are not straight between the engine driven fuel
pump and and fuel selector. I also had a 1/4" return line which I changed to
3/8", the supply line is of course 1/2". I get many of my lines from a local
drag racing place here in Memphis. Those guys really know fuel pressure like
no one else. All my fittings are mil spec AN fittings. My lines are steel
braided, smooth bore Teflon (all custom lengths). The fact that I increased
the volume (at least to the Andair fuel selector) helps the pressure drop when
retarding the throttle. You will still have a slight rise but, nothing like
before. So, go all straight and use a 3/8" return line. I actually lengthened
the lines a bit too. Made for an easy installation. Many guys are out there
flying with fuel flow but, no fuel pressure indication. They never even know
they are getting the increase. It makes sense though because you are still
supplying the same amount of fuel to the pump if you are running at 2400 RPM
but, suddenly you pull back the throttle and the fuel must go through the
bypass in the pump back to the selected tank on a Continental engine - you get
a rise of fuel pressure as the fuel suddenly has to return to the tank through
a smaller line. It took me two months, hope this saves you plenty of time. Oh,
you can just use a no. 4 to no. 6 adapter out of the pump and then a 6 to a 4
back into the fuel selector to accommodate the 3/8" line. I initially wrote to
the Lancair mailing list but no one answered at the time. Both Andair and the
NASCAR guys said, "get rid of any 45 or 90 degree fittings, go straight and
use a larger return line". If you would like some PICS please email me at
waynefmarshall@comcast.net. I live in Memphis and my plane is at AWM (N54KM).
All the best.
 
  Blue Skies, Wayne
 
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