The oil pressure in the gallery feeding the lash adjusters should be at 10-15 psi to operate correctly in the upper rpm range. That's why the restricter was installed in the head, to limit the oil pressure. Did yours survive the rebuild? At lower rpm (idle to 2500 rpm) the lash adjusters should still have time to bleed down even with 50 psi.
Are you getting 50 psi at idle when cold or hot? 1 bbl or 4 bbl? Have you checked to see if you have spark at each cylinder by pulling off the plug wires when running (insulated pliers)? Which cylinders aren't firing? Have you done a compression test? And what are you meaning when you say not firing properly; at all or intermittently?
