I think it most likely flooded when you last tried it and didn't think fuel was flowing into the carb and maybe it was, and when you got the air bubbles clear maybe more. regardless of when it happened it's pretty easy to flood a nitro. (sometimes called "hydrolock") take the plug out as was mentioned to clear it out. what i do in order to prevent more fuel from going into the carb when upright or upside down is take the fuel line off the carb and put it on the tank pressure outlet..this way you have a closed loop and fuel wont exit the tank.

you may want to turn the idle needle up higher to help keep it from stalling out. after you make some progress with running/breakin you can adjust it back down to where it should normally be, but up high helps it from stalling on a new engine.