i had the same stalling issues during my breakin also. this continued until the engine was at or above 200* until breakin was complete. i wasn't able to get around it by leaning or richening the settings, i just had to deal with it. i'm sure it has alot to do with the pinch and rich settings needed to lube the engine during breakin. i also had to leave my ignighter on the car until the temps were around 200*. are you pulling off the ignighter once the engine starts? if so, then the plug is most likely getting cooled off by the incoming full and your seeing what is called flame out.