Hi Nilo,#1 when the engine is inverted if the spray bar is on the fuel tank center line all stays the same,if inverted and the spray bar is a little below the tank center the engine will be a little rich #2 very seldom with glow engines,the pressure from the muffler pressurizes the tank #3 probably but I don't know,the big problem is as the planes goes inverted and there is a large difference in tank/spray bar relations then the engine can get to lean causing damage,or get to rich causing a dead stick,also some engines have problems getting fuel if the fuel lines are more than 12" long,#4 the pump helps in the distant from the tank to the engine ,but not the height of the tank from the spray barHope this is a little help if not ,check back ,someone else might explain it a tad better.