running rough for first couple of minutes
 

2000 454 mag mpi mag runs rough after it has sat for a week or better, runs like the fuel filter has been changed out. After start up and it has ran for a couple of minutes at idle it slowly cleans up and runs fine. The first time this happened i throttled it up a bit and it struggled to throttle up and ran like crap just as if there was air in the fuel system then it cleaned up and ran fine for the day, let it sit over night for about 14 hours started it and it started and ran fine. I keep leaning towards a fuel drain back issue i changed the fuel filter out just before this happened from a napa filter to a mercury 35-802893T. Is there a check in the system somewhere or could this be a different issue any help is much appreciated thanks Lon