From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: [LML] Re: Altitude Switch -- how's a guy to know?
To: lml
Date: Wed, 31 Jan 2007 16:27:30 -0500
Message-ID: <web-1802665@logan.com>
In-Reply-To: <785416.44184.qm@web34909.mail.mud.yahoo.com>
References: <785416.44184.qm@web34909.mail.mud.yahoo.com>
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Posted for bob mackey <n103md@yahoo.com>:

   Jeff:
   If the engine (including injectors, fuel servo, etc)
   only works when fed fuel of just the right pressure, then
   the airframe's fuel system must supply fuel of just that
   pressure.

   To my way of looking at the system... The IO-550/Lancair system
   as describe here has both an engine problem and a fuel delivery
   problem.

   As an example of fuel-system responsibility consider the
   cases in which stagnant hot fuel and vaporizes
   causing vapor lock ar least insufficient fuel delivery.
   The simple solution to that problem is to pump the fuel
   from the tank to a pressure regulator near the injector servo,
   and return the regulator excess to the tank. It works in your
   car, even with much more volatile fuel.

   As an example of engine fuel injection problems, I submit
   that if changes in the fuel pressure delivered to the injector
   servo cause the engine to run unacceptably rich or lean,
   then the injector servo is not doing its job. I don't have
   a Continental IO-550, and I am not familiar with its operation
   other than what I've read here. What I have read here makes me
   think that the fuel injection is overly sensitive to fuel
   pressure variation.

   For comparison, the carbureted Lycoming O-320 in my LNC2
   changes fuel flow by about 4% (13gph max vs 12.5).
   Not enough for a noticeable change when ROP,
   At 12500 ft, I cruise LOP at about 6.5 gph, Again, changing
   the fuel pressure by switching the pump on has little effect.
   If I remember correctly, the fuel pressure varies from about
   20 to 35 psi (or whatever units the EI FP-5L reports).
   The system works because the carburetor's bowl, float, and needle
   regulate out the pressure changes. I did just replace a leaking
   needle/seat, so the 4% variation might have gone away.

   For further comparison, the engine in my Toyota MR2 hasn't run
   noticeabley rich or lean for the last 175,000 miles.
   There has been no service of the fuel system for 17 years.


"""
   Are you certain it is an engine issue and not a fuel system issue?
   
   Regards,

   Jeff Edwards
   LIVP N619SJ
"""