I've been using my BillyGoat KD512SP (w/5.5 HP Briggs & Stratton

Quantum) for quite a few years now, and have noticed a consistent 'burnt oil' smell along with 'smoke' coming from the oil fill tube after it's run for 20 minutes or so. I maintain regularly - oil changes, etc. At first I thought it was burning off excess oil, but as far as I can tell anyhow, the oil is not over-full. Any ideas as to why this may be happening?

It always seemed to run pretty hot. It doesn't get much use per year, probably 10 hours total, mainly from late Oct. through first snowfall. Usually in (very) low 40-50 degree temperatures. Then briefly again in the early spring to do some clean-up. I want to make sure it lasts - it was a pretty expensive unit! So if it's something I'm not doing, or should be doing, I'd appreciate any pointers.

Thanks in advance.