ok after all the GREAT advise about an engine quiting after removing the Batt, i have my own problem

i have the origanal BMJR Stunt Champ ,about 3 years old .origanally had a Brodake 25 dieselized ,.flew great untill the engine faided ,as a glow it had too small of a tank. the tank was uniflow. and it was down on power.

this week i installed a new 3 oz standard vented tank and an FP25  engine has plenty of power ,but the problem is that from a dive, uprite or inverted the engine go's dead rich . i tried capping both vents one at a time and tried with both open. the engine has a standard OS 25 venturi ,so what am i doing wrong