Are your spark plugs wet or dry after trying to start it?
If you have to keep the pedal down to barely get it running, it sounds like it is getting flooded. The pedal opens up the throttle butterfly and allows more air to mix into the cylindars. If your spark plugs are wet after attempting to start, then it is either getting too much fuel (starter injector stuck on) or there are crossed spark plug wires. Also check your static timing, on the '78 it is 5 degrees after top dead center. If the spark plugs are dry, check all of the hose connections and the EGR valve electric solenoid connection.
Kris '78 Vert