912 UL Low Fuel Pressure and Power Loss

Dan,

Is this a new build that has had this problem from the start, or is this a new problem that started after some flight hours?  

Hi Jeff

It's a new build. 

Hi Dan

i would ask what type of airbox are you using.  The vents must go to atmospheric air, not low or high pressure.  As a test simply pull the vents out of the airbox to check that.  If this is a low wing you for sure must have a fuel pump, aux pump, near the fuel supply.  

The mechanical fuel pump must be no older than 5 years, the diaphragm may not be reliable past that.  

Cheers

Hi RW,

"The vents must go to atmospheric air, not low or high pressure." 

I stand to be corrected -the carby float bowl vents should go to /terminate in the same air pressure as the carburettor inlet air ie carby float bowl and inlet air pressure should be the same.

If I am correct, you should have  included  in your statement above - relative to carburettor inlet pressure not "atmospheric"  persay😈

Hi Dan,

I have a similar problem in my Sonex.

I get occasional drops in Cruise, boost pump off, fuel pressure (boost pump is on for anticipated high engine power or low flight conditions)

I have never had any engine hesitation/power loss symptoms - my Dynon tells me I have low pressure, check the fuel pressure gauge and it is indeed low.

If I have sufficient altitude, I ignore the warning and pressure slowly returns. If low, I turn on my boost pump for an immediate pressure recovery.

I  have applied similar "fixes" as you have -

 - I now have all fuel supply lines, in cowling, well insulated and a heat shield on my gascolator.

-  After reading about similar problems in RV 12's,  I installed their solution, a higher pressure/flow rate boost pump.

- Reinstalled the original #35 fuel return line restrictor jet.

- One point you have not mentioned - under cowl temperatur - I have got mine down, from 25C above ambient, to 10C above ambient. To do this,  I incrementally increased the size of the exit air vent.

All of the above have reduced the incidence of low fuel pressure  - can now do several flights without a low warning.

In my case , I think the problem may be an overly complex fuel supply system ( three tanks/fuel selector & very compact boost pump/bypass all in a small space = restriction) causing occasional low pressure.😈