no codes

new plugs turn black quick, running too rich

I have had myself, shade tree mechanic and three legit mechanics, a Ford only specialty shop where the owner did the diagnostics and cant figure it he has 22 years at Ford before opening his shop a few years back

????

everyone is stumped,

low vacuum
build up of carbon on valves and rings

No definitive issue,

even pulled the cam to read it an make sure it wasnt swapped or indexed improperly and all was good even had newer chain

looked at distributor to see if wrong or timing off but all was good...

???

If I don't do the carb swap how do I fix it when no one knows the cause of the symptoms?

 

It's something simple, I hate to tell you that but it's true.

Have you done a compression test? Tested spark to each cylinder?

Low vacuum is indicative of broken rings, severely worn out rings, or a gaping vac leak. Because it's running rich, I'd assume it's one of the former vs the latter. Vac leak wouldn't cause rich issues.

 

Possibly unrelated, but do the trucks use the Mustang style salt and pepper shakers?

Cleaning the 10 Pin connectors on a Mustang | The Mustang Stop

Your first paragraph of the original post is textbook for this.

 

No they do not.

 

Excessive rich is typical fuel regulator or the vacuum line to it. Higher vacuum pulls the pressure down to basically lean it out at idle/cruise.

You put a new regulator on it, but does it work? Have you tried using a vacuum pump on it? Put a gauge on the schrader valve and look for changes. I'm thinking it should be around 38-40 with no vacuum? Something like that.