I just use a garden hose and some Simple Green. Wet the engine down, spray on the Simple Green, and scrub lightly with a brush. Then rinse it with lightly flowing water. Start it up and let it dry out a bit.
Obviously you don't want to drown your electrics, but a lil water shouldn't kill them.
Engine Before (when I first got it)
Engine After
You can't beat Simple Green. Get the spray liquid, not the foam.