[Daves55Sedan]

For erratic misfires, check the following:
Carburator choke operation, choke butterfly should open as engine warms up.
Carburator idle/fuel mixture setting. With engine running and a vacuum guage connected to manifold vacuum, turn idle-mixture screws to get both the highest vacuum reading and smoothest engine idle. Start with screws turned all the way in and back out 1-1/2 revolutions. Vacuum reading should be around 19-20 and NOT erratic.
Carburator float setting. If float is stuck such the level of fuel in the chamber is too low to fire all the plugs, you may need to re-adjust float setting, but first, test fuel pump output. If fuel pump cant pump enough gas to the carb, fix or replace pump and leave carb float alone.
Vacuum. Check all hoses for cracks and fittings for looseness. Try to utilize as much metal tubing in the system as possible rather than replacing with rubber hoses. The old Fomoco products used as much metal tubing as possible in their vacuum systems. Good idea. It would be a good idea to replace old dried out vacuum hoses for the accessories like windshield wipers, heater temperature control system and windshield washer if so equipped. Make sure no original hoses are missing from the accessories.
An easy way to find out if you may be losing vacuum from the accessory circuit is to disconnect and plug the metal tubing leading into the firewall. Doing this will isolate the accessories system from the engine vacuum altogether. Then, get your engine vacuum straightened out first. After you are satisfied with that, go back and re-connect you main accessory vacuum hose and re-check vacuum results. If you now have low or erratic vacuum, something is amiss in your accessory system, right? !
Valve operation. Sticking valves may be causing the problem. Pop the rocker arm covers off and closely watch each valve make it's full travel with engine idling. Note: might be a good idea to rip off long pieces of aluminum foil from the little lady's kitchen so you can use them to cover over the exhaust headers as oil will squirt out of the rocker arm tops.
If any valves look like they are hanging up, you may have a bent valve or bad valve guide. Time for head rebuilding at which time you can redo valve seats too, grind valves and lap valves into seats, check for broken or weak valve springs. If a valve spring is weak, you can use proper size and thickness of washers to beef up the spring tension to specs.