oil residue

I don't think that you should be getting oil residue from the oil breather pipe. I too was getting some oil residue on the underside of the airframe so I fashioned a catcher bottle just using a regular 500ml fizzy drinks bottle and just cable tied it in place. After several flights there was no oil in it. I then discovered that the oily residue was courtesy of the exhaust and not the oil tank.

Kevin it is residue from the bypass. My exhaust is on the opposite side. 

In my opinion, if you are getting that much oil residue down that line, something is wrong.  Usually it seems to be from overfilling, but there are other possibilities.

https://www.rotax-owner.com/en/912-914-technical-questions/8553-oil-vent-trap

Tyler it is not overfilling either.  We keep it at the lower range of the dipstick because anything over 1/2 way just blows out.

I neglected to mention this is not a stock 914.  It has a big bore kit with fuel injection, a welded crank and intercooler.  We get around 140HP all the time if needed but we dont run it that hard all the time.  Only on emergency climbs and initial climbout.  

To clarify I have seen tons of the rotax get the spitting out to oil pressure relief line.  I just find it really, REALLY, annoying to have to clean it off all the time!

IDK, with all those bigger, better things, maybe you need a bigger, better oil tank to match...