1992 300 CE Fuel Delivery Issue

[moohampshire]

When the car sits for a week or two this is what happens. It starts fine and then runs for about 15 minutes with no problems . Then it starts to die on accerlation and finally just dies. From there it is very hard to start. Once I get it running it will run crappy for a little while and then runs fine. If I run the car every day as a daily driver then I have not problems. What can it be. Run only premuim fuel.

Thanks