1994 Kia Sephia shakes and dosent start

Hi I have a kia Sephia from 1994, everything works well, but sometimes I have a problem starting the car, basically I try to started and it trys to start but dosent turn on, then if I press the gas pedal starts but seams to go in 2 or 3 pistons it shakes and some black smokes come out, if I gas a little bit more it goes well, same happens when I drive starts to shake and dosent have power, also sometimes smells of fuel in car.
I change the sparks, for me is like dosent get fuel, I am not sure.