Is it possible that not enough valve clearance can cause a misfire and afterfire (out exhaust) when engine is run steady at higher rpms? It idles fine and revs easily. A valve job was just done and the valves must have seated some. The cold spec for the 4.2 liter is.004 intake and.006 exhaust and when I just checked them they were about.002 -.0025 on the intake and.003 -.005 on the exhaust. I'm restoring the car and it wasn't running when I got it. Almost everything on the motor has been rebuilt or is new. I've checked and rechecked everything I can think of but it won't run right. What do you think?