Re: 1986 F250
Sounds to me like the timing is too retarded. When the distributor was replaced, they most likely put it back to the stock timing spec. It could easily have been advanced at some point in the past to give more power/better fuel mileage, so with it set back to stock specs, you will lose the power/better fuel mileage. I would get a timing light and first check it against the spec. Once you have it set to spec, advance it 2 deg. and drive it. If you don't have spark knock problems, advance it 2 more deg. Do this until you start getting spark knock problems, then back off 2 deg. and leave it set there.
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