Early 912 ULS and fuel return lines...

Tyler Hathaway wrote:

I cannot find that part number (P/N 851328) in the Illustrated parts catalog. Is there a newer part number, or was there a typo?

Look on 73-10-00 page 7 ( current edition IPC)

It is item 13 on the list...

https://www.rotax-owner.com/en/support-topmenu/engine-manuals#912-series-engines

Hey!  I think I have just been misquoted!  ?

Tyler Hathaway wrote:

Hey!  I think I have just been misquoted!  ?

Yep!!!

James wrote that,  Not Tyler!!! 

Bill Hertzel wrote:

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.

Bill, the return flow is nowhere near 5 gph. If you install the return line and restrictor (0.35 mm) as Rotax instructs for the 912uls the flow rate thru it at a normal 3.5 psi fuel pump pressure is about 0.48 gph. You must be thinking of fuel injected systems where the fuel pressure is far higher, or folks are installing much larger restrictors than what Rotax specifies. I have been a fluid power engineer for 40 years so I know how to calculate these things. 

That's pretty cool; is there a fairly simple formula based on pressure, orifice size, and (I assume) viscosity?