912 UL in an early Kitfox and fuel return lines

Thanks, Bill, 

Isn't the engine supposed to run even in a nose-high attitude at a reasonable rate of climb? 

I've gone through the carbs several times due to the flooding problem.  The solution to that was engineering and installation of a fuel return line.   

The lines and filters are new from the header tank forward.  That doesn't mean there is not a bad 'new' filter or maybe installed backward by mistake or a bad hose.  I agree a filter check and flow test are next on the troubleshooting list.  This plane is a nose wheel Kitfox.  I think I'll try a flow test with the nose raised off the floor of the shop.  

This poor plane has been a hanger queen and I have done so much work on her that I was hoping to see the plane fly away so I could move on to other aircraft.  

Thanks for the help and advice.  

Jeffrey,

I too have Kitfox Vixen (2003) with a 912ULS I bought more than five years ago, in flying status however with a lot of deferred maintenance.

In upgrading & restoration, I traded my old 1600 hour engine in to SMLA for a new 912 ULS, complete with a fuel line junction block WITH a fuel return line adapter with metering orifice included (the old 1600 hour 912 ULS did not have a fuel return line).  As part of the new engine hanging I bought and installed a fuel return line kit from the McBeans at Kitfox, as well as a metal header tank and a low fuel warning system.  As per Rotax recommendations I also put in a Facet inline electric fuel pump & filter (just before the main fuel shutoff valve...with no bypass or separate check valve).  I use the inline boost pump for takeoff and landing however have overlooked turning on the boost pump on takeoff and it still worked fine with the engine mechanical pump.  So far so good, the engine has not quit or shown signs of quitting in 230 hours so far while in the air.  I did have the engine quit on the runway after landing at least once in some pretty cold weather and I am blaming it on the idle being too slow. (A low idle IMHO is a good thing for descending glide control however I do understand the need for higher idle on the ground to prolong gearbox life.)

Skot

Yes, the engine is supposed to run up to 40° nose up being limited by Oil Return issues.

I am just identifying symptoms, not pointing out discrepancies.

It appears the problem manifests itself with nose-up and high power.

Nose up makes the pumps work harder and High power demands more fuel.

If the fuel supply is just on the edge, the combination of the two pushes it over.

Dropping the nose and throttling back is what is converting your multiple Impossible Turns into Routine Maneuvers.

A  flow test with the tail on the floor would be a good move.

While you have the hoses OFF, a fuel pressure test might be in line.

Flow is more important than pressure.  The Pressure is just an indicator of Potential flow.

A 99% blocked hose will have nearly Zero flow but will show full pressure to a gauge at Zero flow.

As long as you can keep the carbs full, the pressure is immaterial, but we have to put a number on it.

New Lines and Filters...

New hoses are not guaranteed to be clean hoses.  Were they flushed out before installation?

If all testing gives no results, try a flow test of a fully assembled fuel system and see what comes out with the float bowls removed.

The engine is capable of burning 5 gallons an hour or a quart every 3 minutes to BOTH carbs.

The float bowl refill rate should be at least twice that.  A quart every 3 minutes to EACH Carb.

The KitFox Vixen has now found a warm home in my hanger and doesn't want to leave.  The aircraft with an early 912UL and 375hrs came to the shop with fuel flooding the float bowls of both carbs pouring out the vent tubes resulting in extreme rough idle/low rpm operation.  In the past year, she has had a five year rubber replacement, a re-engineered fuel system because she didn't have a return line.  Complete carb overhauls including all the floats, float needles, and associated hardware.  A fuel pressure gauge was added.  An engine monitoring system was added.  I've performed every fuel system test recommended by Rotax and known to man.  I am now looking elsewhere.  The differential compression check is excellent with a range of 84 - 86 at 87 psi.  Borescope inspection showed good crosshatch and good valves in each cylinder.  The new fuel pressure gauge reads a steady 4psi.  The new engine monitor does give a low EGT indication for #2 cylinder at idle.  However, when the throttle is advanced to higher rpm 3800 or better all the EGTs line up.  There is something going on in that #2 cylinder at low RPMs.  Like I said the compression is good 85 @ 87psi.  I have checked both plugs for gap and resistance, they are new by the way, both new spark plug connectors for resistance, and both cables from the coil.  Everything is within limits.  How do I go further and test the coils, DCDI boxes, and trigger coils/stators, etc.?   How about the valve train for the #2 cylinder?  Could there be a bent pushrod or weak or leaking lifter or weak valve springs?  Could sticking valves in that cylinder cause the rough idle and not be a problem at higher RPMs?  This engine doesn't fall in the serial number range of any of the recent service bulletins about these items.  Still doesn't mean there can't be a problem there.  What else could possibly be causing the low EGT, resulting in the extremely rough running at idle that smooths out at higher RPMs?  My frustration level is thru the hanger roof and I have to remind myself that nothing I did during the rubber replacement or other work caused the problem.  She came into the shop running like that.  HELP...!!!