My fuel pressure guage behave exactly the same way-I put it down to vapour lock.
After about 15 minutes it comes back to middle of the green arc.
 

I did however have a problem which the fuel pressure guage alerted me to some time ago. The fuel shut off valve that was installed in my aircraft was a modified ex cessna part cannabilised around 1991. The linkages had gradually degraded over the years such the when fuel was selected on in the cabin the valve was only partially open in the fuel line. Fuel pressure on climbe out were close to zero.

I replaced the valve and old linkages with the Andair fuel selector and new stainless lines. I now have acceptable and consistent fuel pressure indications.

Incidentally now I have the EDM 700 installed I can observe flow rates of around 45-50 litres per hour at high power on climb out even though fuel pressure is low.


Is this the Bernoulli's principle at work in addition to some vapour lock  ?

"In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's gravitational potential energy.[1] Bernoulli's principle is named after the inventor Daniel Bernoulli."



Gerard