You'll want to soak the engine with Gunk or your favorite engine cleaner/degreaser before hitting it with the pressure washer. In my experience, the grime builds up one layer at a time, and comes off the same.
Thanks for all the tips. Yeah apartment living in Los Angeles has a few drawbacks. I used spray nine grez off on my last bike, that worked pretty well.I found it easier but longer to spray straight heavy duty simple green on, let it soak but not dry out, scrub, spray more, scrub. (I use the little brass, stainless and nylon tooth brush sized ones, and assorted rifle cleaning scrubbers for in the fins.) Rinse and repeat. On a complete engine...disassembled spray away! Even better was a degreaser by zep? At home depot next to simple green...it is heavy duty and not skin or lung friendly.