Hey, I have a 92 mustang with a 347 stoker victor Jr heads performer rpm 2 intake 24 lbs injectors bigger mass air and the tb. I put cats on there and tried to retard the timing but it made my test scores worse as of right now it say I am running a little rich. I have an adjustable fuel pressure regulator but it seem to not want to get low enough to pass. Please help Sean

You might be stuck because those heads are nowhere near being emissions legal and can cause this problem.  Have you had a computer tune done?  That might help a little.