Re: Changing 165 fuel delivery

[garwillis@msn.com (Garfield Willis)]

On Tue, 20 Jun 2000 20:57:27 -0400, Shannen Durphey <shannen@grolen.com>
wrote:

>... There's a high
>pressure in tank pump mounted in the reservoir to pressurize the
>rails, and fuel is circulated through a GM efi filter, through the
>rails, and back into the reservoir.  The reservoir is sealed, except
>for one vent line which could be connected to a charcoal canister. 
>...This means that efi is possible without running return
>lines to the main tank, ...
>This reservoir could be used for other conversions too.

Just a cautionary tale... Because experimental aircraft guys hate the
mess of return fuel plumbing (think of what happens when you have 2-3
main tanks, ugh), many have tried to do a small sump/reservoir return
setup similar (sounding anyway) to what you've described above, where
they pump one-directional from the selected tank with a low pressure
fuel pump, into the sump/reservoir, and then pressurize the fuel rails
from there with a high pressure pump which vents excess fuel back to the
reservoir.

What's been the universal problem with those schemes is the fuel pump
adds mechanical energy to the gas while it's recirculating it, and
without the cooling from the larger main tank's surface area, the gas in
the reservoir gradually heats up, vapor pressure drops, bubbles start to
become visible in clear fuel lines, and before you know it, things start
to go to shit.

Now, obviously Merc has this setup working for them, so I don't mean to
say it's impossible (nothin like an "existence proof", eh?), but I
mention our experiences in XA rather to suggest that they must be doing
something quite right, to avoid the problems that have commonly plagued
us in our applications. IOW, there may be dragons here.

Just me dos centavos, amigo.

Gar


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