backfiring through intake, rough idoling, burning rich what do you think on 1991 Ford F-150

have changed spark plugs, fuel regulator changed rotor and cap distributor

Asked by for the 1991 Ford F-150
2 answers
Did you check the timing or do the compression test. Looks like you just changed parts, those things are mentioned for possibilities, nothing about changing on a guess. If it is backfiring, it would suggest the timing is off, but a compression test would tell if it might be a timing chain, or if ignition timing is off it could cause the same issue. Then these had problems with the stator's and ignition modules, but it should be tested unless you have more money then I do, and I don't have much.
Sounds like your fuel/air ratio is running a little rich. You may want to also change out the EGR and PVC valves.