Where is the distributor cap located for a 1990 Mazda rx7?

On the Driver side on the engine, behind the Power Steering. There is a round black or silver piece with two little screw heads in it. Leave those alone... There is a 10mm bolt that allows you to adjust timing (retard/advance) and it's blocked my a factory piece, just break off that plastic piece of crap from the bolt and you can loosen the bolt, then adjust or distributor or the actual name is "Crank Position Sensor".

You can timing the car just like a regular pushrod car. Get your timing light and put the iductive cable on the L1 of the spark plug wire closest to the coil pack.