<VV> intermittent spark

[Ray Rodriguez]

Ok, 

66 95 horse coupe

     Proper voltage (reads 10.5 while idling on the + side of the coil) going into the coil, I  swapped the coil for a known good unit, relocated the coil away from heat, points are new, condenser is NOT new, dwell is set and not changing, timing is set and not changing.  This is the same car and same problem I was asking about before, I just have new info so the question has changed.  

     The engine is running fine, then poof, spark begins to get intermittent and engine stumbles, then often quits.  After quitting the engine was hard to start, once you get it going it often smooths out and runs ok for a bit before it starts to fall apart again.  The primary ignition wire seems ok, we tested it.  Sometimes the car will run fine for an hour or more at a stretch.  
Most of the time the car runs fine till it warms up, sometimes however the problem is present immediately on a cold start.

     What could cause intermittent spark coming from the coil.  The spark is not intermittent only on the plug wires, it is also cutting in and out on coil wire.

Thanks,

Ray Rodriguez III

CORSA 
65 Corsa 140/4
66 500 coupe 95/PG