Before I changed the Fuel filter the car.

HI, before I changed the Fuel filter the car would always start first time even when cold, now I find if I have not run it for say 24 hours the fuel runs back into the tank so it has to pump fuel back into the carby and then it runs well, If I stop for say 4 or 5 hours then it starts first turn. I have checked the hoses and all seem find there is no sign of any fuel leaks, what maybe causing this Thanks Eldred