I have a 7 HP B&S engine that runs good, but I think the piston ring or something is wearing out. I can mow with it and all of a sudden it will smoke like a locomotive for about 15 seconds with that oil burning smell. Then the smoke goes away for 1 to 5 minutes and it happens again. Since new walk behind mowers and replacement engines are not that expensive, do most people just throw away a smokey engine even though it still runs OK?