<snip
 Why design a return less system?  One of the big advantages of using
 the
 rotary is the ability to use a fuel return system!  Yes you have to
 deal
 with routing a fuel return line - no big deal though in the overall
 scope of the project.  The big advantage is that it eliminates
 virtually
 all risk of vapor lock and hot start issues.  This is important
 especially if you want to run winter blend mogas at high altitudes.
 Fuel return also greatly diminishes the possiblility of water
 contamination.  Once that pump is circulating, even modest amounts of
 water in the system are quickly removed from the injectors.

 The same goes for contamination from a 2-stroke oil bolus.  When I go
 somewhere on cross country and fill an empty tank, that is a big
 gulp of
 2-stroke oil that needs to be mixed in.  I try to shake it up, but
 on a
 number of occasions it has not completely mixed, causing quite an
 engine
 stumble.  If it were not for the return line bringing most of that oil
 back to the tank, the engine may have quit and I may never have gotten
 the engine started in time.

 Take my word on this one (and I cant remember ever having said that
 before) - GO WITH THE FUEL RETURN SYSTEM!  Put your EFI pumps in the
 tank if you want, but they will be easier to service outside the
 tanks.
 Put them low, just outside the tank or inside the fuse.  You won't be
 sorry.  I used scrap aluminum to build a nice little cubby that houses
 the valve and both pumps, just forward of the spar on the pilot's
 side.
 makes for a nice cup holder too.  will try to get a picture on of
 these
 days.

 --
 David Leonard

David -

Wow.  That's the kind of feedback I like.  Thanks.

You bring up some VERY good points on returnless system CHALLENGES.
To summarize:
1) vapors in the fuel rail on hot starts
2) purging of fuel contaminates
2a) water from condensation or ethanol
2b) a slug of 2-stroke oil

Of course these could be overcome using various methods, but all add
complexity.  Your comment that a return line is insignificant in the
scope of a project is well taken.

Related to your comments above, return systems have the following PROS:
- self-purging of vapors, water, and 2-stroke oil.
- stirs up the 2-stroke oil in the tanks.
... and the following CONS:
- requires additional fuel plumbing (return line)
- requires mechanical Andair fuel selector

Regarding in-tank vs. external:
- serviceability is important if required frequently - is it?
- is there a significant cost difference?

What's left is *if* PWM is still worth the effort on a return system.

A mechanical regulator is a proven system, but at the cost of 4 amps
of EFI pump power.  Is it worth adding a fuel pressure sensor and PWM
controller to save power? Is it worth 2x(fuel pressure sensor + PWM
controller) for redundancy?

Interesting turn of discussion ... Thanks Rodoc.

Nice paint job.  I see you around Chino occasionally, and I still want
a ride.  :)

-Vince Orton

 From what I've read, the Walbro GSS 341 draws about 8 amps at 43psi.
Some other pumps draw twice this much.

If you must have mechanical, Weldon makes mechanical pumps intended
for EFI, but I suspect the trouble isn't worth it:

http://www.weldonracing.com/product/28-16/34704__4%2B_GPM_Mechanical_Fuel_Pump.html

-Chris Woods

Here is some more interesting stuff on fuel pumps Chris.
I am going to recommend the roller type as it is doing the job
at only 4 amps.

-------------------

I think I found the source for the MSD roller vane pump.

Airtex

Paul Lamar