Like I said I ran thesame setup on the 280 w/o any prob but when i changed to 450 that's when the problem occur.
Tom there's only one vent and its on the very last tank. I came on thesame conclusion that it's drawing more fuel and not enough vents. Another test I did was defuel from the uat and by the way I am using eight cells pack for my fuel pump and I can see that the uat was collappsing too so I think I have to change back to six cells pack.
And yes 450 sucks and powerful engine. I will remove all tanks from the plane and look for seversed plumb.