Are you using the oe ignition system with dizzy cap ?, if so was the engine hot when you cleaned it ?.
Chances are the hot air inside the dizzy has condensed when the pressure washer water hit the dizzy cap so you now have moisture inside the dizzy cap, this causes cross firing, sounds great but not very good for power!!
Clean/dry out cap failing that I would have a wiggle with the CPS conenctor.
As for the oil, I bet it is on the nearside ?, have a CLOSE look at the oil pressure switch, these leak big time, but cheap easy fix, just had it myself.
tabetha