I have a 1990 roller engine in my 1968 mustang..the engine is carburated..i took off my headers and the #4 exhaust port has a built up of what looks like carbon/burnt oil??.and the flange has a little oil around it.All the other ports look clean..The #4 plug doesnt have oil on it and it looks like the rest tan in color..I had a bad plug wire about a year ago...would that cause that added carbon in that one port or do i have something else to be worried bout..car ran great b4 i put it away for the winter..any help would be great

 

Since it ran fine, if it were me I would clean it up and put it together, and do my best to forget all about it.

And yes, a misfiring cylinder will cause buildup, but I would expect this to burn away when the engine is run hard (i.e. good and hot).

 

A trick my grandfather taught me was to pour about a cap full of water into the carb when its running and it will break up the carbon build up and burn it all up. Works great for me.