I was mowing today with my SCAG 36" HYDRO and the motor just starting revving really high. I shut it down right away. As I started inspecting the mower, I took the engine oil cover off and pulled out the dipstick. I didn't have any oil in it. I got it started again, and it revved really high again. I played with the throttle, but it didn't slow down unless I put the choke on. I'm guessing that the missing oil was the problem, but if I play with the throttle adjuster near the motor/carb, I can get the right RPMs and the engine runs just fine. Any ideas what might have happened?