Why would a motor prefer to run pig rich on the passenger side, but not the driver's?

Plugs on the bad side were black and had lots of buildup, the headers are severely corroded on that side, but it likes to run rich.

 

I was thinking possibly an intake manifold leak, one of the plugs were tan, the rest were black.

 

For anyone that searches a similar problem, it was the edelbrock carb. It was leaking somehow into the manifold which didn't atomize properly and needed to be tuned rich to run decent.

The carb was rebuilt by the previous owner and I tore it apart myself and all seemed well. Could've been a crack somewhere.

Swapped a holley in.