1968 cadillac spits, spudders and shakes

This one has the old points and condenser system?
I have had condensers cause this same condition before but your comments of bad gas or carburetor needing work or replacement are very possible.
Is it a specific "timed" miss-fire or does it seem random.
Let me know.
Regards,

Forty years old, an absolute calssic. A fresh carb is always a good choice, don't try to fix it yourself, get a top quality replacement. Look under the hood on a real dark night, with no light around. Any bad plug wires or plugs will show up. A bad plug will make the wire jump spark. Get a good book on the car, I'm not crazy about Hanes, like Chiltons better. For sure find all the fuel filters.

Carbonator or fuel pump could be the problem - I would also change your spark plug wires they are notorious for causing problems like that and can also cause your engine light to go on. If the wires have a crack in them even down in the shaft it will cause this.