rain problem

Every time my car sits in the rain, when I start it one piston gets flooded....so I check witch piston it is by pulling the spark plug out. When I find witch piston is it, I pull the respective injector out (with the motor running) and let the sparks burn the accumulated fuel in the piston (+- 5 secs.), then I put the injector on.....and everything is fine again. I have no AC, so I just have the grill on the deck lid, and the rain pours directly inside the motor compartment. Is it correctc to have no protection agains rain in the grill? If thats correct, what might be the problem??