Curt:
All of Van's recommended settings for the FlightDEK-D180 in an RV-12 are detailed in a document called 12-D180-PRE-SETS.pdf available from the Van's website - http://vansaircraft.com/public/download/RV-12/Dynon/12-D180-PRE-SETS.pdf.
However, without ALSO measuring the fuel being returned from the engine to the tank (with a second fuel flow sensor installed), the FlightDEK-D180 cannot display an truly accurate fuel flow.
Unfortunately, the FlightDEK-D180 has a single fuel flow sensor input. We explain this in the
FlightDEK-D180 Installation Guide, Page 3-10 - 912(ULS) or 914 Installation.
In the FlightDEK-D180, with engine type set to ROTAX, the RETURN setting is a static "offset" applied to the pulses being received from the fuel flow sensor. By experimentation with the K-factor (increase K-factor to lower the fuel flow, decrease K-factor to increase the fuel flow), or the RETURN value, you can get a fuel flow indication that "more closely approximates" your overall fuel usage, but it won't be (can't really be) accurate without measuring the ACTUAL fuel that is being returned to the tank (which varies depending on the conditions - idle vs takeoff vs cruise, etc.).
I’m using a D180 with a Rotax 912 and a Red Cube flow sensor. I have the fuel return line installed from the fuel rail back to the tank. With the return line blocked off I get a pretty reasonable fuel flow and consumption with a K-Value of 65000. With the return line restored, I get a K-Value of 108750. So what do I enter in the Fuel Flow setup screen for K-VALUE and RETRN?