First, the feedback carb on these thing sucks! Next, there is a knock sensor (unplugged or gone bad) that controlls timing no matter where you put the dist. (you can adjust it a little, but not much as the computer over rides it)
What plugs are you running? I decarburize with water trickled down the carb. Obviously, the EGR valve isn't working. (mine went out and I bought a replacement EGR that I didn't use, then found I a new knock sensor and colder plugs that got me by till I sold it 50,000 miles later)