Early 912 ULS and fuel return lines...

I want to call back the statement about a return fuel line kit from KitFox.  I reviewed the instructions from KitFox.  Their design has and I quote, "...route to the return fitting on the engine carburetor balance tube...".  This, at least in my mind, is confusing.  If they are referring to the "compensation tube" between the intake manifolds or some part of the fuel distribution block.  And the kit doesn't seem to include any kind of restrictor jet as shown by Rotax in the IPC or IM.    

They want the orifice/restrictor jet mounted on the compensation tube because it is a solid mounting point and is the highest place before the carburetor fuel inlets thus any vapour/bubbles will rise up and be vented out before entering the carburetors. You can make your own orifice by soldering in a fitting and then drilling a .35mm hole in it. Also add the the annual inpection check list, to verify fuel flow thru the orifice to make sure it is not blocked by debris.

Thanks Roger!

I forgot to say high wing, no header tank, no gascolator (yet) AND wing tanks.

Would feeding air bubbles back into the supply hose would not increase the problem over time due to have bubbles circle around and grow? Or, if there are few bubbles but primarily fuel circling, does that potentially help to raise the fuel temp over time?

We have been without return line and without problems for years. Do we want to change a running system?

One of the reasons for the recirculation line is to help keep fuel moving through the system so it doesn't get hot enough to form vapor problems. Whether you have it or not if there is vapor formation it's going through the carb whether you want it to or not. The recirculation line helps keep cooler fuel moving so fuel doesn't sit in the line and form vapors.

Jeffrey stated:
...route to the return fitting on the engine carburetor balance tube...".  This, at least in my mind, is confusing.  If they are referring to the "compensation tube" between the intake manifolds or some part of the fuel distribution block.

Kind of vague at best, but I believe they are talking about the actual "Fuel Distribution Block" that is located on the Carb Balance Tube.
The Bypass fuel retune line has ~5 Gallons per hour flowing through it.  About what the engine use at WOT and about 10X the flow of an engine at idle.
Dumping the bypass fuel into the Balance Tube would produce a grossly flooded engine in a matter of seconds.