My 77 280 has been sitting for a year and I just got it running tonight. When I crank it up it takes awhile because it's not holding fuel pressure.It will run fine for a minute then it starts skipping. All plugs are firing(they are new) all injectors are working but when I pull the plug wires to see where the miss is, it seems to be that the first three are weak and the back three are fine. Then it will clear out, then go back to skipping. Could the fuel pressure regulator not be letting the first three get enough gas?