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My bad! Yes on top of triple treeI think it is 5 on this schematichttp://www.harpermoto.com/parts-by-motorcycle/1990-2000-moto-guzzi-motorcycles/california-ev-v11-ev-usa-1100-1997-2000/front-fork-en-california-1100-ev.html
Without looking at the parts diagram I'm not certain but is there a 'button' in the middle of the cap on the stem? If so you'll find if you pry it out with a small flat bladed screwdriver there is a 10mm hex in the cap underneath that you use a key in to undo the nut.Pete