Folks if this has already been mentioned please forgive me. Some engines will kick back (especially if slightly flooded as already mentioned) when flipped in the counterclockwise direction and actually try to run in the opposite direction causing the fuel to "blow" back out of the carb. I start my engines with an electric starter most of the time so this isn't a problem for me. If the engine is indeed kicking back and running backwards, then try flipping it clockwise and it will probably kick back and run in the correct direction. If you are starting it with an electric starter then this shouldn't be the problem.

Also, if you are a licensed pilot, then you are used to talking about engine rotation as viewed from sitting in the cockpit. Counterclockwise, as refered to in this case, is as viewed from the front of the engine looking back as opposed to sitting in the seat like we are normally used to. Good luck and hope you get it figured out.