On a reed valve motor (3W or DA) you can get the fuel to spit out of the carb from only two causes. You could have a bad reed, which allows air/fuel to get blown back out of the carb. Or you may have the carb in a position where the prop blast blows over the mouth of the carb and pulls fuel into the air stream. The DA is less likely to have that problem because it has a rear carb and the engine will shield the carb from turbulence in the cowl.