2.0lt vauxhall vectra hard to start?

this is a od one the car starts ok in the moring and drives geart but if u stop her and let it sit for an hour so it is hard to start u have to crank it over for a while and starts with a bit of smoke. if she is still hot starts ok its only when it sits for a while ate starts fine when stone cold. i have tryed new leak off pipes, new injecter seals, a non return valve on the fule line. so any ideas would be geartful.