There have been several good suggestions by others, so please pardon any repetition, but I have some questions/comments:
After replacing or cleaning the spark plugs, are they still sooty after running the engine? And if so, are ALL of the plugs equally sooty?
Do you know what your electric fuel pump output pressure is?
Is the electric fuel pump a positive displacement pump?
Is the electric fuel pump in series with the original fuel pump, and is it always turned on?
Have you checked the fuel line pressure at the carburetor? Depending on the types of fuel pumps used in series, there is the potential for an additive effect on pressure, and if the fuel pressure at the carburetor fuel inlet is too high, it might cause the float valve to shut off at an overly high fuel level in the bowl, or maybe even leak, either of which could cause an over-rich mixture and other symptoms.
Examples of some things to check: Make sure that the carburetor float action is free and doesn't bind anywhere. Also make sure that there is no pinhole or leak in the float itself that would allow gasoline to enter it and cause it to sink or ride too low in the bowl. Double-check the float level. Check the float valve itself for any damage to the needle or seat. Debris in the float valve can hold it open. Make sure the throttle plate isn't loose. Make sure all mating surfaces in the carburetor match up well, with no gaps, and that fasteners are properly tightened. Overtightening can warp carburetor body parts and cause leakage, etc., etc.
The ETW1 carburetor may appear to be a relatively simple carburetor, but it's actually a bit fussy to rebuild (not 'difficult' but it requires good attention to detail, as it's easy to make a mistake or overlook some operational detail). The governor can also be a bit of a challenge to adjust properly, and a special tool is recommended.
A detailed description and overhaul procedure for the ETW1 carburetor and governor can be found in TM9-1826A.
https://dn790009.ca.archive.org/0/items/TM9-1826A/TM9-1826A.pdf (see page 102).
Have you checked the resistance of each spark plug cable?
Have you checked the centrifugal advance for correct operation using a timing light?
Have you checked for play in the distributor shaft bushings? (That could affect the timing and dwell or cause missing.)
Have you checked for any cracks or carbon trails in the distributor cap?
It's possible for an ignition coil or condenser to develop intermittent performance due to heat or vibration, but if you have changed the coil and condenser with no change in symptoms, that problem would be less likely.
As others have mentioned, check for any possible vacuum leaks. The symptoms, such as a rough idle, hesitation, etc., can vary, but vacuum leaks in the intake manifold of a carbureted, non-computer-controlled engine (like yours) will usually will not cause an overly rich mixture, but would instead tend to cause a leaner mixture.