327 randomly runs bad

[Dead Parrot]

Something that happened to me is the mechanical advance occasionally sticking full in. Could lead to bad performance if you adjusted your idle advance when it was stuck full in. When it snaps back to off, you are now probably ATC on idle timing. Or if initial timing correct, all of a sudden you have an extra 12~15* or so of extra idle timing when it sticks on, which will cause a higher idle speed.

Check idle timing when it is running correctly, then check when idle sticks high(you may have to roll back the idle throttle screw to make sure the RPMs are below where the mechanical advance should start coming in). If your normal idle timing now has +14 or so extra, stuck mechanical advance.