With the key off, short the engine STI and engine ground pins on your EEC-V diagnostic port ( top left and bottom left pins as shown in the diagram here http://www.autoemf.com.au/ford_eec5.htm
). This is neatly done with a female spade lug. Then start the car. The computer will hold the revs at around 2,500 rpm and not alter the timing. Hence you can shift the dizzy and set base timing. If you don’t do this you’ll be setting the timing whilst the computer is potentially advancing or retarding it so you can’t be sure what you’ve set it to.