Motor dies after startup.

Since you changed the idle mixture screws and that fixed or masked the source of the problem, it is important to try to figure if the car is now running rich or lean, and under what conditions.

Have you checked the spark plugs for color? (Do you know how to tell rich versus lean on the plug color?) Too bad you did not check plug color after the good drive yesterday.

Is the 'dull rattling sound' like a hollow clatter that is somewhat medium to high pitched in nature? Can you describe it better? And does it get worse the harder you try to accelerate? Is it worse when the moter RPM's are low or high and you try to accelerate?

You should also examine all vaccum hoses coming from either the base of the carb or higher up on the carb body to see if any are leaking.