An unhappy cylinder?

[Blackduck]

Ricky you have two points correct, Corndog has a problem with #4 and there are 4 ports in the carbs.
Now back to your lack of understanding of carb operation.
3 of those ports are transfer ports and only come into operation when the throttle plate is moved, at idle the mixture screw controlled port does the work. As the throttle is opened the transfer ports are uncovered and supply extra fuel. This is control by primary jet size, the actual transfer port size , fuel level in the bowls and air speed across the ports.
There is nothing extinct or old in carb operation, the principles have not changed.
Better design and engineering have improved them form the first carbs.

[Pete]

Up to this point we have all assumed that it is fuel fouled, and that could be the case.
So adjust the idle mix screw in and see what happens.

Does the plug smell of gas? or maybe oil?
Is the fouling dry or wet and does it dry after exposed to air.

Also consider that maybe it is oil fouling not gas fouled. Valve stem seal.