Hi Peter

[A70Duster]

Got to Rat Shack, and get a book on 555 timer and transistors.  The 555 timer
can make a variable width and period square wave.  Use this square wave to
drive a transistor which will "fire" your injectors.  A o'scope is needed for
exact 80% duty cycle.  A voltmeter can roughly give you duty cycle --- if 12
volts goes to the 555 timer, the output would measure 80% of 12 volts, or 9.6
volts ROUGHLY.

See ya,

Mike