Carl,
I have experienced similar problem as you describe. I have the sight tube
between the seat backs, and I often got the same mis-readings and sudden
drops in the air even though I first blew the vent tubes exactly as you
describe.
I suspected that fuel remained in the tube going over the fuel tank (under
the top of the cockpit module) and back up alongside the filler pipe. Even
with my trigear, on the ground there is a slight aft-down pitch attitude, so
a "U" was formed there. Evidently, fuel still remained there at level
cruise.
I have cured the problem by new routing of the gauge tube from the top front
of the cockpit module (where it used to go into the cockpit module). I cut
the tube there, and instead used a copper tube going up along the front face
of the cockpit module, into the right head rest through a hole drilled in
the inner side near the fore left corner of the head rest, and continuing
always up-up-up through the outer side of the head rest near the rear right
corner and joining the original tube further up. Joined to the original
sight tube both ends by inserting the copper tube into it and securing with
small hose clamp. Painted copper tube where visible in colour matching the
upholstery.
Thus, I no longer have the "U" previously exisiting on top of the fuel tank,
and the gauge reads just fine.
///
Have you tried a good side slip after climb-out? Another Europa (monowheel)
here in Norway does that to get rid of the fuel in his "U" in the gauge tube
(I tried it, but my "U" was probably too deep - or perhaps I did'nt dear to
slip hard enough!)
Best regards,
Svein
LN-SKJ (test flying completed - regular airworthiness certificate received)
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