Hi Kevin,
> I was having a similar problem with my 914. Mine was running rough and
> stumbling
at high power, but only at altitudes above 10,000'.
> The fuel differential pressure gauge would drop and engine run worse with more
power applied.
I think my problem is different. The weird thing is that I'm looking at
a *momentary* drop in fuel pressure, during the first few seconds at
take off power. The fuel pressure then comes back up and the engine runs
fine. Now I'm 100% sure that there is sufficient fuel flow (pump and
filters are ok) it is a mystery why the fuel pressure drops. Note here
that I'm referring to the differential fuel pressure. So it looks like
when the turbo pressure goes up, the fuel pressure lags behind, to catch
up a few seconds later. That's why I suspect the fuel pressure
regulator. This is what you could expect when the regulator valve is
"sticky".
I'm also suspecting the carbs (including the carb bowl gaskets). However
it is a bit strange that the engine runs fine after a few seconds. From
your description of leaking carb bowl gaskets I get the impression that
your symptoms were of a more constant nature.
A carb slide with some friction could be an explanation for the
temporary nature of the problem, but I can't see a relation with the
fuel pressure here. If the slide misbehaves, you should't see a drop in
fuel pressure.
I have observed an overall slightly higher fuel consumption, based on
the fuel flow gauge. Having said that, it is a differential flow meter,
substracting the return flow from the main flow. As the main flow is
over 120 liters per hour, it is hard to say whether a measured fuel
consumpion increase of about 1 to 2 liters per hour is real or just a
small deviation in one of the two flow sensors. Also the carbs or entire
engine could be aging and the whole problem might be unrelated to the
power surge in the first few seconds of the take off.
Back to the fuel pressure regulator. I think that it should held
pressure in its reference port (the small hose connector in the lower
shell) but the air is leaking away rapidly, mostl likely internally,
i.e. via the fuel return hose. This would indicate a leaking diaphragm.
Can anyone confirm that this leak in the reference port is indeed a
fault? (This is not so obvious as I can imagine that the designers
choosed to deliberately incorporate a small leak to cope with a
potentially plugged reference port and to use ambiant pressure in that
case as a backup reference).
Frans
|