With the screw out should be the way it works, make no sense the other way.
Time to start looking at the spark as mentioned above you could be chasing the wrong tail. Try a different coil wired directly to the battery and distributor, bypassing the ignition circuit. Also check the plug gap and condition of each one. If it's a 12 volt system, wire direct 12 volts to coil, no resistor wire, same for 6 volts, you are looking for maximum spark. Try adding a 7th plug grounded to the block and one of the plug wires hooked to it, the engine will miss, but you can get an idea of the spark color and size.
Does it smoke? cracked head sucking oil,
Try plugging the exhaust pipe, all the vacuum ports, and carb inlet. The blow air in through a vacuum port and listen for leaks. Not real sure how to do all that, but a fellow I work with had a late model Chevrolet truck tested using a smoke machine very much like that. They found a small crack in the intake manifold not found using the standard methods. A new intake solved all its problems, by the way, the truck ran good till the intake heated up and the crack opened up.
Joe
