UKPassats

I have b5 Passat 1.9 pd engine. If car is parked engine uphill after 12 hours it will start and then stop. I turn key to crank engine then it will splutter into life-1,2,3,4 cylinders. It runs perfectly fine as long as left with engine downhill. Has had new fuel filter fitted, and o ring seal above. I have checked none return valve. I am looking for some advice as to how the fuel drains back or people who have had similar problems. Car has 240,000 miles on clock.