I have a very old HRM 21 SV that has been a great mower, I bought it used a few years ago and have been more than happy with it. Today while mowing, the engine coughed and blew out a big puff of white smoke, then had a burnt oil smell for a few minutes. The engine settled down and ran perfectly while I finished the lawn. After finishing, I reduced the engine speed and let it idle for a few minutes then shut it off. I checked the oil level and upon removing the oil cap, oil gushed out of the engine, and had a slight gasoline odor. I change the oil every year and use Honda 10w-30 oil. My lawn is practically level with a very small area (about 10x10) that is about 30 degrees slope. Thoughts?