Check your ignition and the voltage the alternator is putting out. When the ignition doesn't get enough voltage to fire the plug correctly it can present as an overly rich condition when in facts its just not enough ignition energy to fire the plug correctly.
I once changed the the pulley size on my alternator to stop throwing the fan belt at the top of the track and when I fired it up the tune was different and the data logger was now telling me it was rich so I pulled the plugs and yep they looked rich but I hadn't changed a jet which means the AFR didn't change but the combustion did. I checked the voltage the alternator was putting out and it had now dropped to 13.5v instead of its regular 14v + at idle.
What gap size does your ignition system require?