a pressure washer would be way too much pressure for a bike or one of these engines. it will get water into places that you don't want it to get. it will also blast off decals, stickers and paint that you may want to keep , and it wioll blow the grease out of wheel bearings.
my bikes don't get that dirty, but i use carb cleaner to spray the engine down every once in awhile which will remove oil residue. To wash the frame, i just use a rag and windex, or soap & water and a garden hose. I use windex on the chrome (rims, fenders, chain gurads, etc.)
my frames and tanks get waxed, and my bikes get cleaned quite often. because i don't like things dirty. sometimes my bikes get dusty from just sitting in the garage.
i never ride in the rain and my bikes have never had mud on them.
i don't ride them much, but i like them to look good when i do ride them, and i take them to car shows along with my car, so i want them to always be clean and ready to go.