Pashka,
If you read the last posts and since you are already using the same Magnum 91 engine I will be using on the ST50, since you have mounted the engine invertd and since you are having fuel flow issues, RMazuera and Rodan's setup are important I think i our case.
I just read on the Sullivan product web page that using a header tank improves fuel pressure.
Magnum recommends having the stopper (or tank center line) at the same level or slightly below the carb valve when engine is inverted. Since your plane is already built and you are flying it
if you decide to implement, please keep me posted so I know what not to do [>:]
Jean-Yves