I don't think it's possible to be rich on just "one side" because I think just about every intake, when at WOT, will feed 2 cylinders on each side from 1 circuit of the carb...for example, the front primaries would feed 1, 4, 6, 7. and the secondaries would feed 2, 3, 5, 8. or something similar to that--with most dual planes anyway....single planes would be more like front primaries on carb feed front 4 cylinders, and the secondaries feed the back 4 cylinders...

but, I don't know for sure, if the carb is gummed up or something it could be possible that one venturi is running rich, making 1 or 2 cylinders richer than the rest...

what color is the smoke? Blue/Grey? Black? White?