The clubmans are probably putting an odd curve on your clutch cable, keeping the clutch from engaging fully. Check your cable routing for any tight spots, hard curves, or any other spot that might make it tight. Mine was binding when I put the clubmans on as it went over the triple tree & down between the clocks, creating an odd angle coming out of the lever houseing. While you're doing that, you might as well lube the cable.
Good luck,
Jay in Philly