Question on carb tuning for the track

[Tommy]

My 351W has a Holley DP 600 CFM. It's tuned to run slightly rich when driving on the street. I recently took it for a day at the Gainesville track with the Deep South Cobra Club. We were running counter-clockwise on the track and I noted occasional black smoke from the right exhaust. When I got home, I pulled the plugs. The four plugs on the driver's side looked just about right. The four plugs on the passenger side looked rich with the two in the center looking especially rich (black soot).

I assume the carb is running rich with the excess fuel going to the outside of the turns. To lean it out, I can lower the float level (primary or secondary or both) or go to smaller jets (primary or secondary or both). Where would you experienced track guys start to address this problem without leaning it out too much?