Carb Float Bowl Breather/Overflow

Thanks Jeffry - hadn't considered a possible air entrainment - will do the test you suggest.

"Air is compressible, fuel is not; it should go quickly to rated pressure".

This does not take into account fuel vapour/gas (even a small amount) on the pressure side of the fuel system. If memory serves; I have never seen a Boost/pulse pump go from zero pressure to max whatever in an instant - they always smoothly  increase from zero - ??

FYI - My fuel reticulation system is particularly complex - three tanks, two selector valves and in the area of the Boost pump (can feed from any one of the three tanks) contorted and compressed into a small area - not great!😈

Hi Roger,

"The carb vents are not supposed to be placed in a vacuum or a pressurized position."

I have been dwelling on your advice.

Rather than posative (RAM) pressure, could my carburettors be creating low/negative pressure within the air box???

What might the symptoms/ramifications' be for negative pressure??

 This is my non Rotax airbox installation (Filter is a single K&N):

Hi Sean,

I'm not fully familiar with your particular air intake setup, but many people have their carb vent tubes attached to their airboxes without issue. Yours's looks okay, but I'm not 100 percent sure. Maybe RW will chime in on your particular setup.

Thanks Roger -

I would not expect you to be familiar with my particular air intake setup - its  a "scratch built". The photos are to give you an idea of the set up.

What I am intersted in exploring is, what might be the symptoms for;

 # Relative high airbox pressure - potentially due to positioning airbox air intake at front of cowling opening.

 # Relative low pressure in the air box - potentially caused by an overly restrictive air filter.

Just read RW's response to "Ring Mount - Why?"

"The aircraft were fine when the gearbox was shimmed to max but shortly after some wear internally the engine would vibrate so bad that fuel would spew from the carb vent tubes and shake badly.  This was noted as the pilot would be coming down to just below peak torque on throttle down.  Descents were scarry for some.  The solution, since it was too late for the kits to be changed and the OEM did not want to redesign, was to install the overload clutch.  (circa 2003 large starter and overload clutches were added) This absorbed the inputs internally to allow them to use the ULS with the existing bed mounts."  

Could this be a factor in my fuel spill issue??