Cleaning a Vespa flywheel requires its removal with two speciality tools. It's not that difficult, and takes little time for mechanical do-it-yourselfers who know their way around a scooter.
Loosen the plastic cylinder cover and flywheel fan cover on the engine by unscrewing the removing screws. Catch the securing screws by hand as they come loose and place them in a metal pan for safekeeping. Remove the engine cylinder and fan covers completely.
Reinsert one screw halfway into the top of the engine case to provide an anchor for the flywheel holding tool (this stops the flywheel from spinning when you loosen or tighten it). Slip the flywheel holding tool onto the screw once it is tight in the engine case. Lock the other end onto one of the flywheel fan fins.
Place a socket wrench onto the flywheel securing nut. Crank the nut loose until it spins freely. Remove the nut and the serrated washer underneath and place them in the metal pan. Insert the flywheel nut tool into the centre of the flywheel. Twist it into the threads inside the flywheel centre. Tighten the tool with a socket wrench as it pushes the flywheel fan off the crankshaft.
Pull the flywheel fan off the crankshaft. Catch the woodruff key (a metal half circle) that sits between the fan and crankshaft arm to secure the flywheel. Place the key in the metal plan. Wipe off dirt and dry residue from the flywheel fan with a shop towel.
Move to an open-air space and spray down the flywheel fan with a solvent cleaner. Wash it thoroughly with the spray. Wipe it with paper towels or shop towels. Allow the flywheel to air dry.
Reinsert the woodruff key onto the crankshaft. Line up the clean flywheel with the key by eyesight and push it back onto the crankshaft. Place the serrated washer and flywheel securing nut onto the crankshaft end. Tighten the flywheel again with a socket wrench and the flywheel holder tool, keeping it from spinning. Tighten the nut to the proper torque setting per the Vespa manual factory specifications. Listen for the torque wrench to click when it's tight enough. Reinstall the engine covers.
A standard carb cleaner spray makes a good solvent cleaner, and it dries quickly.
Never try to pull the flywheel fan off with a gear puller or similar tool. The fan edges are made of aluminium and will bend easily under the strain before the fan comes loose. Eventually this bending will cause cracks, which can cause the flywheel to shatter when being used by the engine and spinning at a high speed.