Fuel Pressure Problems

This is the current setup. https://www.screencast.com/t/mweCPRAR2bm

Ernie

Roger, I know this is an old post, but I have a question related to it.  My 912ULS does not have either an electric pump nor the pressure relief "return" line to the header fuel tank.  I'm preparing to add these to my RANS S-6ES, and trying to figure out the simplest way to do so...  It looks like the Facet 40106 pump (32 GPH, 4.0–7.0 PSI, no check valve, no positive shutoff) would be the right pump to use.  My questions are:

1) What "restrictor" size should I use for the return line?

2) Given that the Facet 40106 is of a "flow-through" design that does NOT inhibit the free flow of fuel thorugh the pump when it is turned off, would it be acceptable to simply plumb it in-line between the gascolator and the existing engine-driven mechanical fuel pump?  Or would the mechanical pump inhibit fuel flow to the engine if it were to fail?

3) Are the fuel lines for the 912 ULS 1/4" internal diameter?  

Also, as an aside, for a high-wing airplane with wing tanks, if the mechanical pump fails, would the engine continue to run as long as there is positive head pressure from the fuel tanks to the carburetors?  (I know this isn't the "best practice", just curious.)

Thanks!