Adjusting base timing by rotating the cams? Where did you learn that? If you want to adjust your base timing by popping the valve cover, you need to do this.
http://www.store.yahoo.com/phase2mot...tosetcaso.html
I'd double check it by checking the timing with a timing light afterwards. Read the FSM on how to do it that way. Shit, even the method above is in the FSM.
Read your FSM next time or do a search.