The sensor plate lifts because of the pressure difference caused by the increased airflow as you open the throttle. More throttle means more airflow means more pressure drop means the plate lifts higher means more fuel pressure to the injectors means more fuel sprays into the ports.

The fuel system normally runs at a fairly high pressure. To decide whether or not the problem really is pressure-related, you must attach the designated pressure gauge to the control pressure regulator and make meaningful measurements.

The control pressure regulator is mounted on a small bracket, which is bolted to the side of the block. The CPR is positioned just behind the distributor. It has two fuel lines attached using banjo bolts (don't drop the copper washers!), one electrical connection (it's a bitch to disconnect), and one inverted "J" hose, which is only a vent to atmosphere.

It's difficult to get to and work on the CPR, but with the distributor cap 'n rotor removed, you can get small hands in there. The most frustrating task is removing the Allen head (metric) bolts that hold the CPR to the bracket. (It might be easier to unbolt the assembly from the block and remove the bracket-with-CPR together.)
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Don Foster (near Cape Cod, MA)