Beer in line seems flat?

I am just getting my long draw home system up and running.... at first things where flowing fine... nice head, good carbonation, ect. Now it seems that if I let the line inactive for even an hour the beer has no carbonation. I can tell you that I am pushing my beer through a 1/4" silicon tubing, the system has an 8' rise, the 20' beer line is completely refrigerated to the tap head and I am pushing 25 psi through the line. (i have tried numerous dif psi's) The beer on tap is Yeungling lager. I have read all the post on balancing the system but have had limited success. I originally thought that maybe I was over carbonating? Anyone have any thoughts? -Jason