The stylish Piaggio Fly 150cc marries a single-cylinder, four-stroke engine to an automatic transmission and electric start, while its 12-inch wheels give it stability and its adjustable rear suspension helps even out the bumps in the road. Checking the spark plug on your scooter provides helpful information on your engine performance; replacing an old spark plug with a new one assures your engine uses a strong spark for combustion. Changing the spark plug isn't complicated, but you'll want to do it correctly to avoid damage to the engine.
Use a screwdriver to loosen screws and remove the scooter body panel underneath the seat front above the floorboards to expose the scooter engine cylinder (the part with the piston inside). Locate the spark plug wire and follow it to the cap connected to the spark plug on the cylinder. You may need to remove one of the small adjacent side panels as well for access. Remove the spark plug cap, being careful not to tear it off. Put it out of the way.
Place the socket wrench and socket over the spark plug in the engine cylinder. Press down on the socket wrench so that the socket is seated properly. Firmly but slowly rotate the socket wrench counterclockwise until it loosens. Spin the old plug out until it comes out of the cylinder threads completely. Put the old plug aside.
Take a shop rag and carefully wipe the cylinder threads and plug cavity without letting anything fall into the hole. Insert the new plug into the cylinder threads and by hand-twist it clockwise, making sure the plug screws in properly into the threads. Do not force it. Remove and redo the installation by hand if the plug starts wrong.
Put the socket wrench on the inserted plug when it cannot be tightened any further using your fingers. Make sure the socket seats properly. Slowly turn the wrench with one hand clockwise until the plug won't go further. Turn it one-quarter more of a rotation to make sure it's tight but don't over-tighten. Place the spark plug cap on the newly installed plug. Press down on the cap so it secures properly. Close up the scooter and test-start the engine.
It's always good to keep spare spark plugs and a socket wrench in your glovebox for a roadside breakdown (the compartment located behind the legshield). Sparks plugs eventually develop build-up or wear down with use and a quick repair can be made by swapping in a new one.
Don't over-tighten the spark plug. Ratchet socket wrenches easily tighten fast, so it's better to use a non-ratchet socket wrench and tighten by hand. If the cylinder threads get stripped, the engine will need to be opened and the cylinder cap repaired to fix the damage.