how can I fix my renault clio 1.4 rt? it starts and runs but won't start ag?

'93 clio it will start and run ok but if you stop it it doesnt want to go again you have to crank it on full throttle and then it will fire on 1 cyl then 2 and then after awhile it will pick up and run perfectly I have replaced the plugs,leads,cap,arm,coil,ecu and the carb . I tested it for spark and its fine the petrol seems to be getting through its almost like something is failing a bit then coming right and working ok.Could this be anything to do with any sender units? please help i'm at my wits end thanks

K Stacey
February 2007