Franz
> Ok, once I started to suspect that I didn't have an air leak but just boiling
fuel, I decided to do a simple test (should have thought about that earlier):
I connected one of these glass filters to the fuel inlet of the engine, so I
could see what the engine was getting.
>
> While the inlet filter looked like I was pumping foam, the filter at the inlet
of the engine showed that the engine was only getting liquid fuel, without a
single bubble of air...
>
Congratulations for this example of practical engineering sense.
All 914 owners will benefit from such experiments.
> Now I have determined that I have no air leak but simply that my fuel is
> boiling
due to underpressure at the suction side of the fuel system, I have some further
questions:
>
> 1) Is this nornal, or do I have bad fuel, or for some reason too much
> underpressure
that is causing this? With other words, do I have a problem?
> 2) At altitude, the pressure will be even lower, hence the fuel will boil
> earlier.
Today is a nice fall day, but the temperatures are nowhere as high as I'm
going to experience during my flights in the south of Europe. Isn't it likely
that some of the vapour bubbles will make it into the carbs once the conditions
go "worse"? Once you have vapour, the bubbles tend to grow rather than to
dissolve. It just doesn't look good that the fuel is already boiling at this
comfortable
but not too high a temperature at 10 ft AMSL...
>
>
We regularly fly over the French Alps at FL 130+ with no problem.
I imagine you won't have to climb that high to clear terrain every day
in the Netherlands ;-)
The point is, the fuel pressure at the carbs is higher than airbox
pressure, so the fuel won't be boiling and any vapour bubble will be
collapsed by positive pressure.
*But* there is always the risk that the pumps be starved should the
"boiling" become too intense at the tank pickup. As already said, the
only real cure is to *push* fuel and not *draw* it up to the pumps.
But this often implies a major redesign of the fuel tank and fuel system.
Best regards,
--
Gilles
http://contrails.free.fr
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