When painting plastic parts on motorcycles, use the proper sanding materials and the proper type of primer and paint. Plastic is delicate and needs careful treatment or you will ruin the mudguards when sanding them. There's no need to spend hundreds and even thousands of pounds to have your plastic motorcycle mudguards painted when you can do it yourself. Painting plastic differs from painting metal motorcycle parts so attention to detail is needed.
Sand the paint off of the plastic motorcycle mudguard by using a 400-grit sandpaper. Continue to sand until you have most of the paint off of the plastic mudguard.
Pour the rubbing alcohol over the plastic. The rubbing alcohol will wash away the sanded paint and loosen up the remaining paint.
Continue sanding until you have removed the paint that remains.
Take the 220-grit sandpaper and wet it with water. Start sanding the surface of the plastic until the surface is completely smooth with no pits. Take a rag and wipe away the sanding dust.
Put two to three coats of the epoxy primer with flex agent on the motorcycle mudguard. Continue adding the primer until the surface has a smooth finish and let the primer completely dry.
Start spraying the acrylic paint with flex agent on the mudguard. Add as many coats as you wish to reach the desired colour.
You must use primer and paint that has a flexing agent in them so that the primer and paint will flex with the plastic.
Do not sand too aggressively or you will have pits in the mudguard that you will have to fill in with a plastic filler.
Always wear safety glasses when sanding and painting.