74 450 was running sluggish and missing. Checked plugs, and #4 and $8 were black (rich). Other plugs were tan/grey normal.
Changed #4 and #8 to rebuilt injectors. Started car up, very small improvement, a little disappointing. Then adanced timing,
and wow- what a difference- much improved acceleration.
Did this w/o a timing light (don't know where mine went).
Since the car definitely does not knock or ping on acceleration,
I would think I'm o.k. (not damaging valves ???). I do currently have 91 octane gas in it- can I go to 89 or 87 w/o knocking?
As I recall, these 4.5's have very low compression, correct?