Fuel system woes

Hi gents,

I have a basic fuel system setup:

high-wing aircraft with wing tanks, fuel lines routed to a left-off-right fuel tank selector and a single line going to the mechanical fuel pump on my Rotax 912 ULS. There is no return line, the only 'extra' is a fuel pressure sensor.

I have always had issues starting the engine after it has been shut down and having waited 20 mins or so.

Today I decided to do some more investigation and kept my EFIS on after shutting down the engine. I noticed how the fuel pressure was constantly rising after around 10 mins, reaching 1 bar (15 psi) peak. I previously thought I was experiencing vapor lock but now I am quite convinced this high pressure is causing the carbs to flood and also flood the cylinders. Would you guys agree with that diagnosis?

It seems the mechanical pump has a check valve which restricts the fuel pressure from bleeding back into the tank.

Since installing a return line is not feasible (the tanks are not really reachable), I was wondering what options I have.

One simple idea would be to add a t-piece and a drain valve on the pump's output side, which I would open after engine shutdown and let the fuel drain below the cowling. Not very eco friendly and quite risky, should I forget to close the valve.

Another idea: add a 0.6mm line between the pump's output and input side, allowing pressure to bleed off but not enough to cause fuel supply issues to the carbs.

Any other ideas or feedback on my ideas?

Many thanks

Mark