Clio backfires through the carb?

Hi, I have a Renault Clio 1.4 on a K plate (1993) , it kept over heating and found it was a faulty thermostat, replaced it but the car wont start. It keeps backfiring through the card (like a spirting/popping sound) I changed the spark plugs thinking it might be them but still no change. Can anybody please help ? thanks