Starting problems when hot on hyundai coupe 1.6 1999

my hyundai starts ok first time but throughout the day as the engine gets hotter its starts to play up! it is ok first time and say i have driven 4 a bit i go 2 start it and it wont start! i then leave it say 20 mins and it starts! more recently it has stalled whilst i am at junctions! i have changed the crank shaft sensor but still doin it! but clock is now workin! he he! can anybody help?!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!