912 ULS Issue on takeoff

Make sure the orifice in the return line is not plugged and is actually returming fuel.

After you have checked the fuel line just to rule out the less likely check there is nothing floating around in the fuel tank.. An avgas stickers has been known to cause similar issues.

I wouldn't recommend flying with an intermittent fault although if it's vapour issues this might be diagnosed by shutting down using the fuel tap and seeing if the problem persists. 

Michael -- The fuel tank vent tip and return orifice tip noted above are good things to check -- in many installations you can hear the fuel returning to the tank by listening through the fuel filler port.  All I can add at this point is that I experienced somewhat the same issue recently and I suspect it to be some contaminated mogas that likely temporarily plugged up some orifices within one of the carbs.  Disassembly and cleaning of the carb appears to have solved the problem. -- David

Ken, there is a vent pipe that comes out the top of the tank next to the return line, that then routes down and out on the bottom of the fuselage. 

It might be worth checking the Throttle Wide Open rpm in the take-off run (high speed taxi).  The minimum should be 5,200rpm.  If its much lower, it may be a cause of the reduced fuel flow that others allude to as the cause of your symptoms.