I have a os155 pumped motor in my large scale space walker. when i do some maneuvers where i roll the plane inverted the engine blows smoke and falters . If I do same maneuver later in flight when tank is about 1/3 full . the engine runs good ? i thought with a pumped engine there would not be a problem like this ! The tank is in normal position behind bulkhead and the center sits just above carby {the motor is inverted} Any clues Help would certainly be appreciated Thank You